Menu
Field Equipment You Will Want for Rockhounding
Layered clothing suitable for the weather
Hat and/or umbrella,
Good shoes/boots suitable for walking on rocky and steep hills,
Gloves to protect hands from sharp edges on the rock,
Walking stick to help with balance on steep and rocky surfaces,
Drinking water, minimum 2 quarts per person, more if it is a hot day,
Lunch,
First aid kit for minor cuts and scrapes,
Maps and guide books to help you get to the collecting site.
Backpack, buckets, and cloth bag to carry the rocks you find
Rock pick/hammer, to dig out and break rocks
Pry bar to pry out rocks,
Sledge hammer and chisel to widen cracks and loosen rocks
Shovel to dig the dirt from around the rock,
Small trowel,
Spray bottle of water to wash off the rock face to help determine if you want the rock,
Wire-screens to separate crystals, quartz or garnets from the dirt or sand,
Vehicle suited to the collection site. Always go with a friend.
Resources:
USGS Quad Maps
BLM and USFS maps
Guide Books
Rockhounding Idaho
Gem Trails of Idaho
Road Side Geology of Idaho
http://geology.isu.edu/Digital_Geology_Idaho/
http://imnh.isu.edu/digitalatlas/geo/fossils/fossils.htm
http://imnh.isu.edu/digitalatlas/geo/gsa/papers/gsac5p17.pdf
http://www.idl.idaho.gov/mining/rockhounding/
http://www.idahoutdoors.com/rock-hounding-idaho/
Hat and/or umbrella,
Good shoes/boots suitable for walking on rocky and steep hills,
Gloves to protect hands from sharp edges on the rock,
Walking stick to help with balance on steep and rocky surfaces,
Drinking water, minimum 2 quarts per person, more if it is a hot day,
Lunch,
First aid kit for minor cuts and scrapes,
Maps and guide books to help you get to the collecting site.
Backpack, buckets, and cloth bag to carry the rocks you find
Rock pick/hammer, to dig out and break rocks
Pry bar to pry out rocks,
Sledge hammer and chisel to widen cracks and loosen rocks
Shovel to dig the dirt from around the rock,
Small trowel,
Spray bottle of water to wash off the rock face to help determine if you want the rock,
Wire-screens to separate crystals, quartz or garnets from the dirt or sand,
Vehicle suited to the collection site. Always go with a friend.
Resources:
USGS Quad Maps
BLM and USFS maps
Guide Books
Rockhounding Idaho
Gem Trails of Idaho
Road Side Geology of Idaho
http://geology.isu.edu/Digital_Geology_Idaho/
http://imnh.isu.edu/digitalatlas/geo/fossils/fossils.htm
http://imnh.isu.edu/digitalatlas/geo/gsa/papers/gsac5p17.pdf
http://www.idl.idaho.gov/mining/rockhounding/
http://www.idahoutdoors.com/rock-hounding-idaho/
Rockhounding Eastern Idaho
The majority of rocks collected in Eastern Idaho are agates and jaspers associated with Challis Volcanic rhyolite flows and petrified wood associated with ash fall tuffs and welled tuffs. In addition to the Challis Volcanics, other rock and minerals of interest are : 1) The plutonic rocks consisting mainly of granite that contain quartz and feldspar crystals, 2) The metamorphic rocks containing garnet, serpentine and marble. 3) Sedimentary limestones containing horn coral and cronoids and clam shells. Several geologic events have shaped Eastern Idaho, Inland seas that resulted in the deposition of thick layers of limestone, up lift of the Pioneer Mountain and Idaho batholiths, basin and range faulting, Challis volcanics, Yellowstone hotspot migration and glaciers.
Rocks are formed on Earth as igneous, sedimentary, or metamorphic rocks. Igneous rocks (plutonic and volcanic) form when rocks are heated to the melting point which forms magma. Sedimentary rocks are formed from the cementing together of sediments, or from the compaction (squeezing together) of sediments, or from the recrystallization of new mineral grains which are larger than the original crystals. Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock.
Rocks are formed on Earth as igneous, sedimentary, or metamorphic rocks. Igneous rocks (plutonic and volcanic) form when rocks are heated to the melting point which forms magma. Sedimentary rocks are formed from the cementing together of sediments, or from the compaction (squeezing together) of sediments, or from the recrystallization of new mineral grains which are larger than the original crystals. Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock.
Plutonic Rocks
Granites are the most abundant plutonic rocks of mountain belts and continental shield areas. They occur in great batholiths that may occupy thousands of square kilometers and are usually closely associated with quartz monzonite, granodiorite, diorite, and gabbro. Granite is a light colored plutonic rock formed when a bulge of magma, called a batholith, pushes up the rocks above but does not reach the surface and cools slowly allowing the minerals to grow into individual crystals visible to the naked eye.
Granite consists of coarse grains of quartz (10-50%), potassium feldspar, and sodium feldspar. These minerals make up more than 80% of the rock. Other common minerals include mica (muscovite and biotite) and hornblende (see amphibole). The chemical composition of granite is typically 70-77% silica, 11-13% alumina, 3-5% potassium oxide, 3-5% soda, 1% lime, 2-3% total iron, and less than 1% magnesia and titania.
Granite is used as a building and ornamental stone. Many ore deposits (copper, lead, zinc, gold, and silver, for example) were produced by hydrothermal solutions created during late stages of cooling of granite bodies. These may be emplaced around the peripheries or related to fissures and fractures within bodies of granite
Granite consists of coarse grains of quartz (10-50%), potassium feldspar, and sodium feldspar. These minerals make up more than 80% of the rock. Other common minerals include mica (muscovite and biotite) and hornblende (see amphibole). The chemical composition of granite is typically 70-77% silica, 11-13% alumina, 3-5% potassium oxide, 3-5% soda, 1% lime, 2-3% total iron, and less than 1% magnesia and titania.
Granite is used as a building and ornamental stone. Many ore deposits (copper, lead, zinc, gold, and silver, for example) were produced by hydrothermal solutions created during late stages of cooling of granite bodies. These may be emplaced around the peripheries or related to fissures and fractures within bodies of granite
Metamorphic Rocks
In this area are located on the edge of the batholiths or volcanic craters where the heat, pressure, water and gases created by the batholiths and molten magma in the craters altered the host rocks.
Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage. Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock. Slate, as an example, will split into thin sheets.
Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage. Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock. Slate, as an example, will split into thin sheets.
- Slate is a fine-grained metamorphic rock with perfect cleavage that allows it to split into thin sheets. Slate usually has a light to dark brown streak. Slate is produced by low grade metamorphism, which is caused by relatively low temperatures and pressures.
- Schist is a medium grade metamorphic rock. This means that it has been subjected to more heat and pressure than slate, which is a low grade metamorphic rock. As you can see in the photo above schist is a more coarse grained rock. The individual grains of minerals can be seen by the naked eye. Many of the original minerals have been altered into flakes. Because it has been squeezed harder than slate it is often found folded and crumpled. Schists are usually named by the main minerals that they are formed from. Biotite mica schist, hornblende schist, garnet mica schist, and talc schist are some examples of this.
- Gneiss is a high grade metamorphic rock. This means that gneiss has been subjected to more heat and pressure than schist. Gneiss is coarser than schist and has distinct banding. This banding has alternating layers that are composed of different minerals. The minerals that compose gneiss are the same as granite. Feldspar is the most important mineral that makes up gneiss along with mica and quartz. Gneiss can be formed from a sedimentary rock such as sandstone or shale, or it can be formed from the metamorphism of the igneous rock granite.
- Quartzite is composed of sandstone that has been metamorphosed. Quartzite is much harder than the parent rock sandstone. It forms from sandstone that has come into contact with deeply buried magmas. May look like agate but will look sugary when broken.
- Marble is metamorphosed limestone or dolomite. Both limestone and dolomite have a large concentration of calcium carbonate (CaCO3). Marble has many different sizes of crystals. Marble has many color variances due to the impurities present at formation. Some of the different colors of marble are white, red, black, mottled and banded, gray, pink, and green.
- Serpentine The name serpentine is used for both a mineral and a metamorphic rock. It is formed by the metamorphic transformation of olivine and pyroxene to the serpentine mineral group. Serpentine varies from a light green to a dark green color with veins and fractures. It strongly resembles some varieties of jade.
- Jade is applied to two different metamorphic rocks that are composed of different silicate Minerals: Nephrite consists of a microcrystalline interlocking fibrous matrix of the calcium, magnesium-iron rich amphibole mineral series tremolite (calcium-magnesium)-ferroactinolite (calcium-magnesium-iron). The middle member of this series with an intermediate composition is called actinolite (the silky fibrous mineral form is one form of asbestos). The higher the iron content, the greener the color. Jadeite is a sodium- and aluminium-rich pyroxene. The gem form of the mineral is a microcrystalline interlocking crystal matrix.
Introduction to Fossils
Note: The collecting of fossils from animals that had a vertebra (back bone) is not allowed on Public Lands.
Sedimentary Rocks make up a majority of the rocks in Eastern Idaho
Paleontology is the study of plant and animal remains. Paleontologists trace the development of life from its forms more than 600 million years ago through its evolution today. Fossils are the remains or evidence of ancient plants or animals that have been preserved in the earth's crust.
Plants and animals have undergone great change through geologic time. The general trend is toward more complex and advanced forms of life. However, some life forms have not changed and others have become extinct. The succession of life indicates that older rocks generally contain the remains of more primitive life forms and the remains of more advanced life forms are confined to the younger rocks.
Most fossils are found in marine sedimentary rocks. Only a very small fraction of prehistoric plants and animals have left a record of their existence.
Three requirements must be satisfied for ancient life to be preserved as fossils:
1 . The organism generally must have hard parts such as shell, bone, teeth or wood tissue;
2 . The remains must escape destruction after death; and
3. The remains must be buried rapidly to stop decomposition.
Very fine-grained sediments are much more proficient in preserving fossils than coarse-grained sediments. Ash-fall tuffs from nearby volcanoes have covered forests near Challis, Idaho. These fossil forests were formed while the trees were still standing.
Fossils are preserved in four basic ways: (1) original soft parts of organisms; (2) original hard parts of organisms; (3) altered hard parts of organisms; and (4) traces of organisms.
Sedimentary Rocks make up a majority of the rocks in Eastern Idaho
Paleontology is the study of plant and animal remains. Paleontologists trace the development of life from its forms more than 600 million years ago through its evolution today. Fossils are the remains or evidence of ancient plants or animals that have been preserved in the earth's crust.
Plants and animals have undergone great change through geologic time. The general trend is toward more complex and advanced forms of life. However, some life forms have not changed and others have become extinct. The succession of life indicates that older rocks generally contain the remains of more primitive life forms and the remains of more advanced life forms are confined to the younger rocks.
Most fossils are found in marine sedimentary rocks. Only a very small fraction of prehistoric plants and animals have left a record of their existence.
Three requirements must be satisfied for ancient life to be preserved as fossils:
1 . The organism generally must have hard parts such as shell, bone, teeth or wood tissue;
2 . The remains must escape destruction after death; and
3. The remains must be buried rapidly to stop decomposition.
Very fine-grained sediments are much more proficient in preserving fossils than coarse-grained sediments. Ash-fall tuffs from nearby volcanoes have covered forests near Challis, Idaho. These fossil forests were formed while the trees were still standing.
Fossils are preserved in four basic ways: (1) original soft parts of organisms; (2) original hard parts of organisms; (3) altered hard parts of organisms; and (4) traces of organisms.
Original Soft Parts of Organisms
At death the organism must be buried and preserved in a substance such as frozen soil, ice, oil, saturated soils and amber. The frozen tundra of Alaska and Siberia has preserved large numbers of frozen woolly mammoths. After being frozen for as long as 25,000 years, their bodies are now exposed to the atmosphere due to thawing. The flesh of some of these creatures has been sufficiently preserved to be eaten by dogs. Fossil insects are commonly found in a tomb of amber.
Original Hard Parts of Organisms
Most plants and animals have hard parts capable of becoming fossilized. These include shells, teeth, bones and woody tissue of plants. These hard parts are composed of substances such as calcite, calcium phosphate, silica and chitin which are capable of resisting weathering and chemical action.
Altered Hard Parts of Organisms
The alteration process occurs during and after burial and the results are determined by the composition of hard parts. The following methods are common:
1. Carbonization- As the organic material decays after burial, gases and liquids are lost leaving only a thin film of carbonaceous material. Coal is formed in this way. Also fish, graptolites and reptiles are individually preserved in this manner.
2. Petrifaction -Fossils are commonly preserved by mineral-bearing ground waters infiltrating porous bone, shell or plant material and converting the material to stone. Calcite, silica and compounds of iron are normally the minerals deposited.
3. Replacement -The original hard parts are dissolved and removed by underground water. Simultaneously the original structure may be replaced by substances such as calcite, dolomite, silica and iron compounds.
4. Traces of Organisms - Shells, bones, leaves, tracks, burrows and trails are commonly preserved as molds or casts. If a shell or track is pressed down on the ocean bottom while the sediment is still soft, an impression called a mold is left. If this impression is later filled with another material, a cast is produced.
1. Carbonization- As the organic material decays after burial, gases and liquids are lost leaving only a thin film of carbonaceous material. Coal is formed in this way. Also fish, graptolites and reptiles are individually preserved in this manner.
2. Petrifaction -Fossils are commonly preserved by mineral-bearing ground waters infiltrating porous bone, shell or plant material and converting the material to stone. Calcite, silica and compounds of iron are normally the minerals deposited.
3. Replacement -The original hard parts are dissolved and removed by underground water. Simultaneously the original structure may be replaced by substances such as calcite, dolomite, silica and iron compounds.
4. Traces of Organisms - Shells, bones, leaves, tracks, burrows and trails are commonly preserved as molds or casts. If a shell or track is pressed down on the ocean bottom while the sediment is still soft, an impression called a mold is left. If this impression is later filled with another material, a cast is produced.
traces of organisms
Fossils Indicate Environment of Deposition
Fossils are used to trace the development of plants and animals through geologic time. We have learned that fossils become progressively complex and more advanced in younger rocks. Fossils are valuable for indicating the environment of deposition of the surrounding sediments. For example, reef corals indicate deposition in warm, shallow salt water. Fossils also indicate the depth, temperature, bottom conditions and salinity of ancient seas.
Correlation of Rocks with Fossils
One of the most important uses of fossils is to correlate or match rock layers separated by many miles. If a similar assemblage of fossils is found in both layers, it may indicate the two layers are related to each other. To be useful for correlation, a fossil should have a very limited vertical range (period of living) and a wide horizontal range (geographic distribution). This means that a fossil lived in a short time in geologic history but was widely distributed during its short life. This type of fossil is called an index fossil or guide fossil.
Fossils are used to trace the development of plants and animals through geologic time. We have learned that fossils become progressively complex and more advanced in younger rocks. Fossils are valuable for indicating the environment of deposition of the surrounding sediments. For example, reef corals indicate deposition in warm, shallow salt water. Fossils also indicate the depth, temperature, bottom conditions and salinity of ancient seas.
Correlation of Rocks with Fossils
One of the most important uses of fossils is to correlate or match rock layers separated by many miles. If a similar assemblage of fossils is found in both layers, it may indicate the two layers are related to each other. To be useful for correlation, a fossil should have a very limited vertical range (period of living) and a wide horizontal range (geographic distribution). This means that a fossil lived in a short time in geologic history but was widely distributed during its short life. This type of fossil is called an index fossil or guide fossil.
FOSSILS OF IDAHO
Paleontology and Fossils
This information was taken from "Exploring Idaho Geology" by Terry Maley (1987). New dating and estimates of duration of geologic periods (i.e. Cambrian) in the last 15 years has revised some of the ages listed here.
Paleontology is the search for knowledge about past life through the study of the evidence (fossils) preserved in the geologic formations of the earth. It is the basis of the geologic time scale and of the correlation of formations on a worldwide basis. New methods of dating formations have refined the time scale but have not changed the correlation's based on the fossil evidence.
This evidence of life covers all of the five kingdoms presently defined in the study of life. The five kingdom system (monera, protista, fungi, plantae, and animalia) was developed by R. H. Whittaker of Cornell University. This system is generally accepted by biologists today, but is still not perfect. Nature seems to have an aversion to pigeonholes.
The present system, as well as all previous systems, leaves viruses out in the cold even though viruses are definitely organic and contain complex molecules. The new system is still an improvement over the previously used two kingdom system (plants and animals), the three kingdom system (protista, plants and animals, or the four kingdom system (protista, fungi, plants, and animals).
The newest system adds the kingdom Monera. This kingdom includes bacteria and cyanobacteria (blue-green algae). These life forms are biologically unique and did not fit well into the old classification systems. This uniqueness includes the lack of a nuclear envelope and membrane-bound organelles.
Monera are also paleontologically unique as they represent the oldest fossils ever found on the earth and are responsible for our oxygen enriched atmosphere. Evidence of the existence of this simple form of life can be traced back 3.5 billion years. About 10,000 species have been described but some question this and believe that less than 3,000 distinct species actually exist.
The oxygen produced as a waste product by the monera did not become immediately available for use of other types of organisms or for the development of an oxygen enriched atmosphere. The Archean (3.8 to 2.5 bybp) and proterophytic (2.5 to 2.0 bybp) oceans were rich in free iron (bybp means billion years before present). Precipitation of this iron in banded iron formations had to occur before free oxygen could become readily available for other uses. It was not until well into the Proterozoic (2.0 to 0.57 bybp) that changes in the environment allowed the next important advance in life to occur.
The fossil record for the Late Precambrian is very poor. Evidence that is available indicates that the kingdom protista and the kingdom animalia developed during this time period. All of the representatives of the animal kingdom during the Late Precambrian were soft bodied.
The discussion of the various formations in Idaho and their associated fossils comes from a review of many geologic and paleontologic references dealing with Idaho. Those sources reviewed during the preparation of this discussion represent only a small portion of the existing literature.
Many fossil genera and species are not mentioned because the scope of this discussion is not appropriate to a complete listing of all genera and species known from Idaho.
This information was taken from "Exploring Idaho Geology" by Terry Maley (1987). New dating and estimates of duration of geologic periods (i.e. Cambrian) in the last 15 years has revised some of the ages listed here.
Paleontology is the search for knowledge about past life through the study of the evidence (fossils) preserved in the geologic formations of the earth. It is the basis of the geologic time scale and of the correlation of formations on a worldwide basis. New methods of dating formations have refined the time scale but have not changed the correlation's based on the fossil evidence.
This evidence of life covers all of the five kingdoms presently defined in the study of life. The five kingdom system (monera, protista, fungi, plantae, and animalia) was developed by R. H. Whittaker of Cornell University. This system is generally accepted by biologists today, but is still not perfect. Nature seems to have an aversion to pigeonholes.
The present system, as well as all previous systems, leaves viruses out in the cold even though viruses are definitely organic and contain complex molecules. The new system is still an improvement over the previously used two kingdom system (plants and animals), the three kingdom system (protista, plants and animals, or the four kingdom system (protista, fungi, plants, and animals).
The newest system adds the kingdom Monera. This kingdom includes bacteria and cyanobacteria (blue-green algae). These life forms are biologically unique and did not fit well into the old classification systems. This uniqueness includes the lack of a nuclear envelope and membrane-bound organelles.
Monera are also paleontologically unique as they represent the oldest fossils ever found on the earth and are responsible for our oxygen enriched atmosphere. Evidence of the existence of this simple form of life can be traced back 3.5 billion years. About 10,000 species have been described but some question this and believe that less than 3,000 distinct species actually exist.
The oxygen produced as a waste product by the monera did not become immediately available for use of other types of organisms or for the development of an oxygen enriched atmosphere. The Archean (3.8 to 2.5 bybp) and proterophytic (2.5 to 2.0 bybp) oceans were rich in free iron (bybp means billion years before present). Precipitation of this iron in banded iron formations had to occur before free oxygen could become readily available for other uses. It was not until well into the Proterozoic (2.0 to 0.57 bybp) that changes in the environment allowed the next important advance in life to occur.
The fossil record for the Late Precambrian is very poor. Evidence that is available indicates that the kingdom protista and the kingdom animalia developed during this time period. All of the representatives of the animal kingdom during the Late Precambrian were soft bodied.
The discussion of the various formations in Idaho and their associated fossils comes from a review of many geologic and paleontologic references dealing with Idaho. Those sources reviewed during the preparation of this discussion represent only a small portion of the existing literature.
Many fossil genera and species are not mentioned because the scope of this discussion is not appropriate to a complete listing of all genera and species known from Idaho.
Late Proterozioic
The Late Proterozoic time period lasted for 330 million years (1000 to 540 mybp). Multicellular animals such as protomedusae, hydrozoa, anthozoa, octocoralla, and annelida developed in a shallow-water environment. Cyanobacteria continued to be an important life form.
The fossil evidence of monera in Idaho exists in the form of stromatolites. Stromatolites are laminated masses of calcareous rock formed by mat-like communities of cyanobacteria and other monera. Being the only level of the food chain allowed for a tremendous population to develop during the Proterozoic. Unfortunately, there are no published articles dealing specifically with Proterozoic or later monera in Idaho. Those articles that do happen to mention the presence of monera represent passing references to stromatolite structures or beds and their utility or lack of utility in geologic correlations and the study of pateoecology.
Late Proterozoic formations are the oldest fossil bearing formations in Idaho.
The fossil evidence of monera in Idaho exists in the form of stromatolites. Stromatolites are laminated masses of calcareous rock formed by mat-like communities of cyanobacteria and other monera. Being the only level of the food chain allowed for a tremendous population to develop during the Proterozoic. Unfortunately, there are no published articles dealing specifically with Proterozoic or later monera in Idaho. Those articles that do happen to mention the presence of monera represent passing references to stromatolite structures or beds and their utility or lack of utility in geologic correlations and the study of pateoecology.
Late Proterozoic formations are the oldest fossil bearing formations in Idaho.
Cambrian
The Cambrian time period lasted for 65 million years. The moderate to shallow marine waters of the Cambrian System were an excellent environment for a tremendous explosion of life forms. The first sponges, jellyfish, tabulate corals, brachlopods, chitons, gastropods, cephalopods, nautiloids, bivalves, hyolithids, trilobites, crustaceans, ostracods, crinoids, echinoderms, conodonts, graptolites and other marine life forms come from Cambrian deposits.
The Cambrian System in Idaho is represented by formations extending from southeastern Idaho to the Pend Oreille area of northern Idaho. The sediments and the fossils indicate that a broad oceanic shelf existed along the western margin of the existing continent. Idaho was completely underwater during this period.
The Cambrian System in Idaho is represented by formations extending from southeastern Idaho to the Pend Oreille area of northern Idaho. The sediments and the fossils indicate that a broad oceanic shelf existed along the western margin of the existing continent. Idaho was completely underwater during this period.
Ordovician
The Ordovician time period lasted for 67 million years. Moderate to shallow water marine environments continued to produce an explosion of new life forms. The greatest diversification was in the invertebrate animal kingdom at the genera and species levels. The first rugose corals, bryozoa, Strophomenide brachiopods, Spiriferide brachiopods, Rhynchenellidae-type brachiopods, starfish and vertebrates show up in the Ordovician along with new cephalapod subclasses, bivalve subclasses and others.
The first vertebrates are placed in the Ordovician because fossil fish of the class agnatha have been found in Ordovician deposits. There is the possibility that conodonts represent the first vertebrates or chordates. Small tooth-like and plate-like calcium phosphate remains are all the evidence we have of the conodonts. Such evidence is inconclusive.
The Ordovician System in Idaho is well represented in the central and southern part of the state. A continuation of the marine shelf environment is indicated.
The Genera and species of graptolites are too numerous to list completely. Some of the more important Ordovician genera include Didymograptus, Isograptus, Glossograptus, Climacograptus, Pleurograptus and Dicellograptus.
The first vertebrates are placed in the Ordovician because fossil fish of the class agnatha have been found in Ordovician deposits. There is the possibility that conodonts represent the first vertebrates or chordates. Small tooth-like and plate-like calcium phosphate remains are all the evidence we have of the conodonts. Such evidence is inconclusive.
The Ordovician System in Idaho is well represented in the central and southern part of the state. A continuation of the marine shelf environment is indicated.
The Genera and species of graptolites are too numerous to list completely. Some of the more important Ordovician genera include Didymograptus, Isograptus, Glossograptus, Climacograptus, Pleurograptus and Dicellograptus.
Silurian
The Silurian time period lasted for 30 million years. Where life forms expanded into deeper water during the Ordovician as compared to the Cambrian, they began to colonize the land in the Silurian. Most of the major invertebrate life forms are already present. The protista Dinoflagellata and the Pteridophyta and Psilophyte types of vascular plants show up in the Silurian. Hippuritoida mollusca, arachnids, barnacles and terrestrial arthropods also first show up in Silurian deposits along with a great variety of fish.
The Silurian system in Idaho is represented by formations cropping out in the central and southeastern part of the state. The sediments and associated fossils indicate the presence of continued nearshore shelf sedimentation and coral reef building.
The Silurian system in Idaho is represented by formations cropping out in the central and southeastern part of the state. The sediments and associated fossils indicate the presence of continued nearshore shelf sedimentation and coral reef building.
Devonian
The Devonian time period lasted for 48 million years. The shelf sea continues to produce a great variety of stromatoporoids, brachiopods, corals, cephalopods and ostracods. The monograptids die out in this period as do most of the trilobites. The first mosses, liverworts, lycopods, ferns and gymnosperms show up in the Devonian. The first terebratulid-type brachiopods, scap4opods, ammoinoids, coleoids (belemnites), mytiloids (mussels), unionoids (fresh water bivalves), brachiopods, hexapods, placoderms, chondrichthyes, and amphibia show up in the Devonian.
Idaho was still under water during the Devonian. We therefore have none of the land forms mentioned above represented in Idaho formations. The Devonian system in Idaho is represented by formations cropping out in the central and southeastern part of the state. Erosion has removed all other traces of this system in Idaho. The sediments that remain indicate moderate to shallow water marine deposition.
Idaho was still under water during the Devonian. We therefore have none of the land forms mentioned above represented in Idaho formations. The Devonian system in Idaho is represented by formations cropping out in the central and southeastern part of the state. Erosion has removed all other traces of this system in Idaho. The sediments that remain indicate moderate to shallow water marine deposition.
Mississippian
The Mississippian or Early Carboniferous time period lasted for 40 million years. The marine environment continues to produce a great variety of life during this period. The increase in the diversity of life occurs to the greatest extent at the genera and species levels. Conifers, Heterocorallia-type corals, Myoida-type bivalves and reptiles first show up in Carboniferous rocks.
Idaho has mostly marine deposits with coral reef faunas well represented. Coarse-grained, distinctive, continentally-derived sediments with associated plant fossils show up in Idaho for the first time during the Mississippian period as a result of the Antler Orogeny. Parts of Idaho were probably not very high above sea level nor were they above sea level for very long.
The Mississippian system in Idaho is represented by formations cropping out in the central and southern parts of the state. Many formations have been named and renamed.
Idaho has mostly marine deposits with coral reef faunas well represented. Coarse-grained, distinctive, continentally-derived sediments with associated plant fossils show up in Idaho for the first time during the Mississippian period as a result of the Antler Orogeny. Parts of Idaho were probably not very high above sea level nor were they above sea level for very long.
The Mississippian system in Idaho is represented by formations cropping out in the central and southern parts of the state. Many formations have been named and renamed.
Pennsylvanian
The Pennsylvanian or Late Carboniferous lasted for 34 million years. Large shallow seas and fresh water swamps created an excellent environment for a great abundance of life. The great swamp forests are todays major coal fields. The plant life was quite diverse and very large when compared to present plant life.
Insects, amphibians and reptiles increased in diversity during this period. Brachiopods, bryozoa and crinoids were abundant. Corals were few and mostly of the solitary type. The blastoids became extinct during this period. An exceptionally large type of foram known as the fussilinid is characteristic of the Pennsylvanian. Trilobites are still around but rare.
The Pennsylvanian system in Idaho is represented by formations in the central and southeastern parts of the state. Tectonic activity during the Pennsylvanian caused uplift and many interruptions of sedimentation. Fossils representing the quality, quantity and diversity of life that existed in the Mississippian were never again repeated in the marine deposits of Idaho. Erosion and metamorphism since the Pennsylvanian has added to the problem of finding good Pennsylvanian fossils.
Insects, amphibians and reptiles increased in diversity during this period. Brachiopods, bryozoa and crinoids were abundant. Corals were few and mostly of the solitary type. The blastoids became extinct during this period. An exceptionally large type of foram known as the fussilinid is characteristic of the Pennsylvanian. Trilobites are still around but rare.
The Pennsylvanian system in Idaho is represented by formations in the central and southeastern parts of the state. Tectonic activity during the Pennsylvanian caused uplift and many interruptions of sedimentation. Fossils representing the quality, quantity and diversity of life that existed in the Mississippian were never again repeated in the marine deposits of Idaho. Erosion and metamorphism since the Pennsylvanian has added to the problem of finding good Pennsylvanian fossils.
Permian
The Permian time period lasted for 41 million years. It was a time of continental-wide tectonic disturbance and climatic changes. The first cycads show up in the Permian. The first Urochordata (sea squirts or tunicates), Archosauria (dinosaurs, crocodiles), Euryapsida (nothosaurs, plesiosaurs, pliosaurs, ichthyosaurs) and the first snyapsida (mammal-like reptiles) show up in the Permian.
The Permian also represents great extinctions. The end of trilobites, conocardiacea-type mollusks, bactritoidea-type cephalopods, rugose corals and hyolithids came during the Permian. All productid brachiopods and most other types also died out as did all of the blastoids and most crinoids.
The Permian System in Idaho is represented by formations in the west and east central areas and the southeast. The formations and fossils indicate a restricted marine environment in the east-central and southeastern parts of the state. The west-central area is characterized by volcanics.
The Permian also represents great extinctions. The end of trilobites, conocardiacea-type mollusks, bactritoidea-type cephalopods, rugose corals and hyolithids came during the Permian. All productid brachiopods and most other types also died out as did all of the blastoids and most crinoids.
The Permian System in Idaho is represented by formations in the west and east central areas and the southeast. The formations and fossils indicate a restricted marine environment in the east-central and southeastern parts of the state. The west-central area is characterized by volcanics.
Triassic
The Triassic time period lasted for 37 million years. It started out with many unfilled ecological niches due to the extinctions of the Permian. Bivalves, including the unionids and oysters became very diverse in the Triassc. New types of gastropods developed during this period including limpets and periwinkles. The scleratinia-type corals which are the most abundant coral today first showed up in the Triassic. The first snakes also showed up during the Triassic period.
Especiallv noteworthy is the development of the first mammals. The mammal record is poor until the Paleocene and the extinction of the dinosaurs. It is, however, evident that by the end of the Triassic, animals with distinctively mammalian oestological features had evolved on the largest single land mass to ever exist.
Very few life forms became extinct during the Triassic. The conodonts, Bellerophon gastropods and the mammal-like reptiles known as paramammals are notable exceptions to the rule.
The Triassic system in Idaho is represented in the western part of the state.
Especiallv noteworthy is the development of the first mammals. The mammal record is poor until the Paleocene and the extinction of the dinosaurs. It is, however, evident that by the end of the Triassic, animals with distinctively mammalian oestological features had evolved on the largest single land mass to ever exist.
Very few life forms became extinct during the Triassic. The conodonts, Bellerophon gastropods and the mammal-like reptiles known as paramammals are notable exceptions to the rule.
The Triassic system in Idaho is represented in the western part of the state.
Jurassic
The Jurassic time period lasted for 64 million years. It was a time of great evolutionary growth in terrestrial life and a time of expansion for shelf seas. World-wide temperatures were moderate.
Pulmonate mollusks (gill breathers) and coccolithophorida developed during this period. Bivalves, gastropods and crustaceans (ammonites) were the major marine organisms inhabiting the continental shelves. Ammonites became widespread and have proven useful in accurate correlation on a world-wide basis. There are 64 zones used in the study of the Jurassic. One for each million years on average.
Reptiles and land plants became quite diverse and widespread. Mammals continued to develop but remained small. The mammal-like reptiles (paramammals) became extinct during the Jurassic. The flying reptiles reached their peak during this period and the first birds developed.
The Jurassic system in Idaho is represented by formations in the western and eastern parts of the state. Erosion has removed all other traces of Jurassic sedimentation in Idaho.
Pulmonate mollusks (gill breathers) and coccolithophorida developed during this period. Bivalves, gastropods and crustaceans (ammonites) were the major marine organisms inhabiting the continental shelves. Ammonites became widespread and have proven useful in accurate correlation on a world-wide basis. There are 64 zones used in the study of the Jurassic. One for each million years on average.
Reptiles and land plants became quite diverse and widespread. Mammals continued to develop but remained small. The mammal-like reptiles (paramammals) became extinct during the Jurassic. The flying reptiles reached their peak during this period and the first birds developed.
The Jurassic system in Idaho is represented by formations in the western and eastern parts of the state. Erosion has removed all other traces of Jurassic sedimentation in Idaho.
Cretaceous
The Cretaceous time period lasted for 79 million years. It was a time of great change for the dinosaurs which reached both their peak and their demise during this time period.
In the protista kingdom at the other end of the scale, life was also changing. Silicoflagellata and Diatomacea began to appear. Diatoms have proven to be very useful for dating later formations. The first angiosperms also appear in Cretaceous times. These flowering plants produce leaves, seeds and pollen. Petrified wood and leaves are the most commonly collected fossil. Fossil seeds are relatively rare. Pollen may be preserved in excellent condition.
The Neogastropoda also developed in the Cretaceous while the Ammonoids which were so widespread and useful during the Jurassic died out. The bivalve order Hippuritoida which developed during the Silurian also passed away by the end of the Cretaceous.
The Cretaceous system in Idaho is only known from the southeastern part of the state. The rest of Idaho was undergoing uplift and erosion during this period.
In the protista kingdom at the other end of the scale, life was also changing. Silicoflagellata and Diatomacea began to appear. Diatoms have proven to be very useful for dating later formations. The first angiosperms also appear in Cretaceous times. These flowering plants produce leaves, seeds and pollen. Petrified wood and leaves are the most commonly collected fossil. Fossil seeds are relatively rare. Pollen may be preserved in excellent condition.
The Neogastropoda also developed in the Cretaceous while the Ammonoids which were so widespread and useful during the Jurassic died out. The bivalve order Hippuritoida which developed during the Silurian also passed away by the end of the Cretaceous.
The Cretaceous system in Idaho is only known from the southeastern part of the state. The rest of Idaho was undergoing uplift and erosion during this period.
Palegene (Paleocene, Eocene and Oligocene)
The Paleogene time period includes the Palcocene, Eocene and Oligocene epochs. It lasted for 43 million years. Many important changes in life occurred during the Paleogene, especially in terrestrial life.
The great Cretaceous extinctions made room for a great expansion of the survivors. This expansion generally started out slowly in the Paleocene but by the Oligocene had gained a good momentum. The complexity of this radiation, the voluminous literature associated with it, and the lack of evidence in the Idaho fossil record precludes much of a discussion of it here.
Idaho has been a land mass since at least the Early Cretaceous. Except for fresh water and volcanic deposition, Idaho has been eroding throughout the Cenozoic.
The earliest record of fossil remains from the Paleogene of Idaho, which I have been able to find, is a plant record. Angiosperms which include Monocots and Dicots possibly began in the Jurassic. They are definitely known from the Cretaceous and by the end of it are undergoing a significant expansion. Much of the work by early paleobotanists identified fossil leaves using the well-known geologic principle of "the present is the key to past." Early angiosperms, however, may not have modern keys. Identification made on the gross characteristics of specimens that do not have the fine venation patterns preserved are open to question. Most of the work published before the 1970's suffers from this problem.
The great Cretaceous extinctions made room for a great expansion of the survivors. This expansion generally started out slowly in the Paleocene but by the Oligocene had gained a good momentum. The complexity of this radiation, the voluminous literature associated with it, and the lack of evidence in the Idaho fossil record precludes much of a discussion of it here.
Idaho has been a land mass since at least the Early Cretaceous. Except for fresh water and volcanic deposition, Idaho has been eroding throughout the Cenozoic.
The earliest record of fossil remains from the Paleogene of Idaho, which I have been able to find, is a plant record. Angiosperms which include Monocots and Dicots possibly began in the Jurassic. They are definitely known from the Cretaceous and by the end of it are undergoing a significant expansion. Much of the work by early paleobotanists identified fossil leaves using the well-known geologic principle of "the present is the key to past." Early angiosperms, however, may not have modern keys. Identification made on the gross characteristics of specimens that do not have the fine venation patterns preserved are open to question. Most of the work published before the 1970's suffers from this problem.
Neogene (Miocene, Pliocene)
The Neogene time period includes the Miocene and Pliocene Epochs. It has lasted for 18.4 million years. Life through this period became increasingly similar to presently Iiving species. Most of the genera still exist today as do many of the species.
Modern carnivores, rodents and ungulates have gone through a period of expansion during the Neogene of North America. The primitive mammalian forms were increasingly headed towards extinction.
Angiosperms were still expanding out into new genera and species. Grasses developed and spread out into savannah lands during this period. Conifer forests, however, have declined in diversity and areal extent.
The Neogene of Idaho is represented in the northcentral and southern parts of the state. There are more published acounts of fossils from the Neogene of Idaho than there are for any other time period. A complete listing of all the general and species identified has not been made but would contain representatives of all the kingdoms of life. The record is especially good for Miocene plants, Pliocene gastropods and Pliocene vertebrates.
The Quaternary time period includes the Pleistocene and Holocene Epochs. It represents 1.6 million years of geologic time from the beginning of the Glacial Epoch to the present. We have made a distinction between the last ten thousand vears and the Pleistocene. This distinction may not be justified. The accuracy of dating earlier periods has not allowed us to define them to so fine a distinction. We may be in an interglacial period of minor importance in terms of geologic time. Life is still adjusting to the last ice advance and retreat. It may have to adjust to a new one.
Modern carnivores, rodents and ungulates have gone through a period of expansion during the Neogene of North America. The primitive mammalian forms were increasingly headed towards extinction.
Angiosperms were still expanding out into new genera and species. Grasses developed and spread out into savannah lands during this period. Conifer forests, however, have declined in diversity and areal extent.
The Neogene of Idaho is represented in the northcentral and southern parts of the state. There are more published acounts of fossils from the Neogene of Idaho than there are for any other time period. A complete listing of all the general and species identified has not been made but would contain representatives of all the kingdoms of life. The record is especially good for Miocene plants, Pliocene gastropods and Pliocene vertebrates.
The Quaternary time period includes the Pleistocene and Holocene Epochs. It represents 1.6 million years of geologic time from the beginning of the Glacial Epoch to the present. We have made a distinction between the last ten thousand vears and the Pleistocene. This distinction may not be justified. The accuracy of dating earlier periods has not allowed us to define them to so fine a distinction. We may be in an interglacial period of minor importance in terms of geologic time. Life is still adjusting to the last ice advance and retreat. It may have to adjust to a new one.
Pleistocene
Life in the Pleistocene was very similar to the life of the present. Some species have either died out completely or have moved out of North America and continued to evolve. We no longer have any native proboscidians, rhinoceroses, camels, llamas, horses or sloths in North America. The mammoths, wooley rhinoceroses and ground sloths have passed on forever.
Pleistocene fossils have been found throughout the state. Not all areas are very productive. The only Pleistocene fossil record that I have found for northern Idaho refers to a single horse tooth found at Moscow in the "Palouse" Formation. I would be happy to hear from anyone who may have Pleistocene fossils from northern Idaho. Almost all of the Idaho Pleistocene localities are either related to the Snake River Plain or are found in Late Pleistocene cave and archeological sites.
Pleistocene fossils have been found throughout the state. Not all areas are very productive. The only Pleistocene fossil record that I have found for northern Idaho refers to a single horse tooth found at Moscow in the "Palouse" Formation. I would be happy to hear from anyone who may have Pleistocene fossils from northern Idaho. Almost all of the Idaho Pleistocene localities are either related to the Snake River Plain or are found in Late Pleistocene cave and archeological sites.
Holocene
The Holocene or Recent time in Idaho covers the last 10,000 years. Deposits containing preserved evidence of past life include swamps, caves, archeological sites and lake bottoms.
Agate and Jasper
Challis Volcanic originated in the area of Challis Idaho and flowed outward covering an area north and east into Montana, east to Arco, south to Carrie and west to Fairfield Idaho. It is estimated that the depth of the flows in the Challis was 2000 feet deep. These consisted of rhyolite, andesite and basalt flows depending on the type of magma extruded. Mountain building, basin and range faulting and erosion have altered the surface over the last 50 million years resulting in our current topography. Volcanic rock of equivalent chemical composition and mineralogy to granite (acidic rocks, high in silica) is called rhyolite. Andesite and basalt are the chemical equivalent of mafic rocks (basic rocks, little to no silica). Therefore the challenge for rockhounds is to find the remnants of the rhyolite flows that are favorable for the deposition of agate and jasper. The majority of agate and jasper found it the Challis Volcanics are in found in rhyolite flows that contain gas pockets and fractures.
What is Chalcedony?
Chalcedony is a generic name given to any material that is composed of microcrystalline quartz. Agate and jasper are both varieties of chalcedony.
What is microcrystalline quartz? “Quartz” is a mineral composed of silicon and oxygen (SiO2) and the word microcrystalline means that the quartz is in the form of crystals that are smaller than 30 microns in size (a micron is a unit of measure that is 1/1000th of a millimeter). These are very tiny quartz crystals – smaller than can be seen by the unaided eye. (Sometimes the word “cryptocrystalline” is used instead of “microcrystalline.”)
Chalcedony is a very hard material. It has a hardness of 7 on the Mohs scale. It breaks with a conchoidal fracture, and freshly broken pieces have a very smooth, non-granular texture and a waxy to vitreous luster. These characteristics enable chalcedony to be cut and polished into a bright, durable gemstone.
Chalcedony occurs in a wide range of colors. It is often gray, white, brown, red, yellow, orange and black, but it can occur in any color. It can also be banded or have plume, dendritic, mottled, mossy or other color patterns. At one time the word “chalcedony” was reserved in parts of the gemstone industry for a light blue translucent material; however, this use of the word has nearly disappeared.
The Difference Between Agate and Jasper
The primary difference between agate and jasper is in their diaphaneity. The word “diaphaneity” is used to describe “how easily light passes through a material.” There are three general levels of diaphaneity. They are, from highest to lowest:
What is microcrystalline quartz? “Quartz” is a mineral composed of silicon and oxygen (SiO2) and the word microcrystalline means that the quartz is in the form of crystals that are smaller than 30 microns in size (a micron is a unit of measure that is 1/1000th of a millimeter). These are very tiny quartz crystals – smaller than can be seen by the unaided eye. (Sometimes the word “cryptocrystalline” is used instead of “microcrystalline.”)
Chalcedony is a very hard material. It has a hardness of 7 on the Mohs scale. It breaks with a conchoidal fracture, and freshly broken pieces have a very smooth, non-granular texture and a waxy to vitreous luster. These characteristics enable chalcedony to be cut and polished into a bright, durable gemstone.
Chalcedony occurs in a wide range of colors. It is often gray, white, brown, red, yellow, orange and black, but it can occur in any color. It can also be banded or have plume, dendritic, mottled, mossy or other color patterns. At one time the word “chalcedony” was reserved in parts of the gemstone industry for a light blue translucent material; however, this use of the word has nearly disappeared.
The Difference Between Agate and Jasper
The primary difference between agate and jasper is in their diaphaneity. The word “diaphaneity” is used to describe “how easily light passes through a material.” There are three general levels of diaphaneity. They are, from highest to lowest:
- Transparent (light and images pass through)
- Translucent (light passes through)
- Opaque (no light passes through)
What is Agate?
Agate is a translucent to semitransparent chalcedony. If you have a piece that is semitransparent you will be able to hold a very thin piece up and see distorted or foggy images through it. If you hold a translucent piece up to a source of light you will see a small amount of light passing through the thin edges. If you hold it up to the light and pass your hand between the material and the source of light, your hand will block the light passing through the material
Agate is generally a banded material, and observing bands in a specimen of chalcedony is a very good clue that you have an agate. However, some agates do not have obvious bands, or instead of being banded they have plume or mossy inclusions.
How Does Agate Form?
Many agates form in areas of volcanic activity where waters, rich in dissolved silica (SiO2), flow through fractures and cavities in igneous rocks. When the solution is highly concentrated with dissolved silica, a silica gel can form on the walls of these cavities. That gel will slowly crystallize to form microcrystalline quartz.
Over time, additional layers of gel are deposited and these form younger bands of microcrystalline quartz on the walls of the cavity. If the dissolved mineral composition of the silica-rich water changes over time, impurities (elements other than silicon and oxygen) can be incorporated into the gel and into the microcrystalline quartz. These impurities can alter the the color of the microcrystalline quartz. This can produce the color banding, plumes or moss that are often seen in translucent agate.
Although agates typically form in igneous rocks such as basalt, rhyolite, and andesite, they can also form in sedimentary rocks such as limestone. All of these types of rock are more susceptible to weathering than agate. So when the rocks are eventually broken down by weathering, the durable agates will remain. This is why agate nodules are often found in stream valleys that cut through fine-grained igneous rocks or limestone.
Agate is generally a banded material, and observing bands in a specimen of chalcedony is a very good clue that you have an agate. However, some agates do not have obvious bands, or instead of being banded they have plume or mossy inclusions.
How Does Agate Form?
Many agates form in areas of volcanic activity where waters, rich in dissolved silica (SiO2), flow through fractures and cavities in igneous rocks. When the solution is highly concentrated with dissolved silica, a silica gel can form on the walls of these cavities. That gel will slowly crystallize to form microcrystalline quartz.
Over time, additional layers of gel are deposited and these form younger bands of microcrystalline quartz on the walls of the cavity. If the dissolved mineral composition of the silica-rich water changes over time, impurities (elements other than silicon and oxygen) can be incorporated into the gel and into the microcrystalline quartz. These impurities can alter the the color of the microcrystalline quartz. This can produce the color banding, plumes or moss that are often seen in translucent agate.
Although agates typically form in igneous rocks such as basalt, rhyolite, and andesite, they can also form in sedimentary rocks such as limestone. All of these types of rock are more susceptible to weathering than agate. So when the rocks are eventually broken down by weathering, the durable agates will remain. This is why agate nodules are often found in stream valleys that cut through fine-grained igneous rocks or limestone.
What is Jasper?
Jasper is an opaque variety of chalcedony. Neither light nor images pass through. Microcrystalline quartz in its pure form is semitransparent. When a small amount of impurities or foreign materials are added, the color of the microcrystalline quartz changes and its ability to transmit light decreases. Jasper contains enough impurities and foreign material to render it opaque. So, the real difference between jasper and agate is the amount of impurities and foreign material contained with a specimen.
How Does Jasper Form?
While agate is typically a material that forms in the cavities of an igneous rock or limestone, jasper forms when fine particulate materials are cemented by silica. This often occurs in soft sediments when silica precipitates and cements them into a solid mass. These included particulates are what give jasper its color and opacity. A sedimentary material known as chert forms in extensive bedded deposits, and as an opaque variety of chalcedony it receives the name “jasper.” Jaspers are also known to form when volcanic ash is cemented into a solid material from the precipitation of silica from solution.
How Does Jasper Form?
While agate is typically a material that forms in the cavities of an igneous rock or limestone, jasper forms when fine particulate materials are cemented by silica. This often occurs in soft sediments when silica precipitates and cements them into a solid mass. These included particulates are what give jasper its color and opacity. A sedimentary material known as chert forms in extensive bedded deposits, and as an opaque variety of chalcedony it receives the name “jasper.” Jaspers are also known to form when volcanic ash is cemented into a solid material from the precipitation of silica from solution.
MINERAL TEST KIT INTRODUCTION
There are over 2000 different mineral species composed of chemical elements or compounds.
Minerals can be identified by testing their properties and through careful observation. Many rock and mineral specimens are actually composed of a mixture of mineral species.
Be sure to test and identify each mineral in a specimen composed of two or more species. Once you have tested a mineral specimen you can identify it by comparing your test results with the mineral characteristics as given in a good rock and mineral field guide.
Minerals can be identified by testing their properties and through careful observation. Many rock and mineral specimens are actually composed of a mixture of mineral species.
Be sure to test and identify each mineral in a specimen composed of two or more species. Once you have tested a mineral specimen you can identify it by comparing your test results with the mineral characteristics as given in a good rock and mineral field guide.
FIELD EQUIPMENT You Will Want for Rock and Mineral Identification
FIELD EQUIPMENT
- Geology hammer/pick
- Holster for hammer (optional but very useful;
- Hand lens (10X)
- Small field magnet
- Small acid bottle (10% HCl)
- Mineral Sample Hardness Kit
- Hard-covered field notebook
- Pencil
- Compass
- Knife or nail
- Penny
- Small triangular metal file
- Plastic bags for specimens
- Permanent Marker
- 5/10X Magnifier
- Ceramic Plate (for streak and hardness test)
- Glass Plate (for hardness test)
- Acid Bottle (for fizz test)
- Magnet (for magnetic test)
- This kit supplies the basic tools necessary for rock, mineral, and fossil identification and includes: streak plate, glass plate, hand lens, dropper bottle, magnet, nail, penny, and harness scale. From Amateur Geologist - $9.15
MINERAL HARDNESS
Hardness is the ability to scratch another mineral or material. The Mohs scale of hardness consists of 10 minerals varying in hardness from 1 through 10, with talc (1) the softest and diamond (10) the hardest:
- Talc
- Gypsum
- Calcite
- Fluorite
- Apatite
- Feldspar
- Quartz
- Topaz
- Corundum
- Diamond
- 2.5 Fingernail
- 3.5 Copper penny
- 5.5 Glass plate
- 5.5 knife blade or nail
- 6.5 Ceramic plate
- 6.5 metal file
THE STREAK OF A MINERAL
A streak is the color of a mineral in powder form.
It is determined by rubbing a specimen across a ceramic plate. The streak is an important identifying characteristic, especially of metallic minerals. The streak of some minerals is similar to the mineral color in lump form. In other minerals that streak is very different from the mineral color. Minerals with a hardness above 6.5 have a colorless streak because they are too hard to leave a streak on the plate.
Wash your ceramic plate with soap and water as necessary to clean it.
It is determined by rubbing a specimen across a ceramic plate. The streak is an important identifying characteristic, especially of metallic minerals. The streak of some minerals is similar to the mineral color in lump form. In other minerals that streak is very different from the mineral color. Minerals with a hardness above 6.5 have a colorless streak because they are too hard to leave a streak on the plate.
Wash your ceramic plate with soap and water as necessary to clean it.
MAGNETISM
Magnetism can be strong, weak or non-existent in minerals. Test magnetism with a magnet. The specimen is non-magnetic if it is not at all attracted to a magnet. It is weakly magnetic if it has a slight attraction to a magnet and strongly magnetic if it has a strong attraction to a magnet.
ACID REACTION
Some minerals are carbonate compounds that dissolve rapidly in acid, producing bubbles or “fizz.”
Test a specimen for this property by placing a drop or two of dilute hydrochloric acid on it. It will produce tiny bubbles if it is composed of carbonate. Dilute 1 part concentrated hydrochloric acid with 3 parts water to make dilute hydrochloric acid. Vinegar will also work, although not as well with some minerals.
Muriatic Acid can be purchased at your local hardware store.
NOTE: Vinegar is a weaker acid but can be used in many applications for limestone and calcite. It will take longer and make fewer bubbles.
Test a specimen for this property by placing a drop or two of dilute hydrochloric acid on it. It will produce tiny bubbles if it is composed of carbonate. Dilute 1 part concentrated hydrochloric acid with 3 parts water to make dilute hydrochloric acid. Vinegar will also work, although not as well with some minerals.
Muriatic Acid can be purchased at your local hardware store.
NOTE: Vinegar is a weaker acid but can be used in many applications for limestone and calcite. It will take longer and make fewer bubbles.
SPECIFIC GRAVITY
Specific gravity is the weight of a mineral compared to the weight of an equal volume of water.
Determine specific gravity by first weighing a mineral specimen to the nearest 0.1 gram (g) using a sensitive balance. Then measure the water volume the specimen displaces when dropped in a graduated cylinder 1/2 full of water. Record the volume to the nearest milliliter (ml) or fraction of a ml. Since the density of water is 1 gram per milliliter (1 g/ml) at room temperature, specific gravity is calculated by dividing the mineral weight by the displaced volume.
Determine specific gravity by first weighing a mineral specimen to the nearest 0.1 gram (g) using a sensitive balance. Then measure the water volume the specimen displaces when dropped in a graduated cylinder 1/2 full of water. Record the volume to the nearest milliliter (ml) or fraction of a ml. Since the density of water is 1 gram per milliliter (1 g/ml) at room temperature, specific gravity is calculated by dividing the mineral weight by the displaced volume.
|
The Idaho Falls Gem & Mineral Society is a non-profit organization promoting the study of geology, lapidary and applied sciences, and fostering a spirit of fellowship among the members since 1957. We are members of both the Northwest and American Federation of Mineralogical Societies (NFMS and AFMS).
|
Photographs and written materials may not be reproduced in any manner without written permission. Copyright © 2026 Idaho Falls Gem & Mineral Society