Obsidian

by Jim Bosley

Description:
Obsidian is igneous rocks formed as a result of magma, the parent material, cooling rapidly above ground, which is the parent material.  Obsidian is actually glass and not a mixture of minerals. Obsidian is the result of volcanic lava coming in contact with water. Often the lava pours into a lake or ocean and is cooled quickly. This process produces a glassy texture in the resulting rock. Iron and magnesium give the obsidian a dark green to black color.  When obsidian is ejected from a volcano and cools rapidly in the air and falls to earth it is known as an obsidian bomb.

Chemistry:
SiO2;  Mostly silicon dioxide with large amounts of impurities.
Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline; in addition, its composition is too complex to comprise a single mineral. It is sometimes classified as a mineraloid. Though obsidian is usually dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. Obsidian consists mainly of SiO2 (silicon dioxide), usually 70% or more. Crystalline rocks with obsidian's composition include granite and rhyolite (parent material). Because obsidian is metastable at the Earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. This breakdown of obsidian is accelerated by the presence of water. Obsidian having low water content when newly formed, typically less than 1% water by weight, becomes progressively hydrated when exposed to groundwater, forming perlite.
Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities.  Iron and magnesium typically give the obsidian a dark brown to black color. Very few samples are nearly colorless. In some stones, the inclusion of small, white, radially clustered crystals of cristobalite in the black glass produce a blotchy or snowflake pattern (snowflake obsidian). It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden sheen (sheen obsidian) or an iridescent, rainbow-like sheen (rainbow obsidian).

Obsidian has been used by ancient people as a cutting tool, for weapons, and for ceremonial purposes and is sometimes found by archaeologists in excavations.   The edges of this rock are very sharp. 

PHYSICAL CHARACTERISTICS:

• Color is dark green to dark brown and black, also can show sheens of gold or green, yellow, blue and/or purple coloration. Sometimes with white inclusions (Snowflake Obsidian).
• Luster is vitreous.
• Transparency: Obsidian is translucent in any stone of appreciable size.
• Crystal System does not apply because obsidian is amorphous.
• Habits include compact nodules or as massive layers between other volcanic rocks
• Fracture is conchoidal.
• Hardness is 5 - 5.5 (much softer than quartz).
• Specific Gravity is approximately 2.6 (average)
• Streak is white.
• Other Characteristics: Generally lacks open voids or large bubbles like other volcanic rocks.
• Notable Occurrences include Italy; Mexico; Scotland; Arizona, Colorado, Texas, Utah and Idaho, USA, as well as the Cascade Volcanic Mountain range and its associated lava beds, which stretches from Northern California into Washington state.
• Best Field Indicators are color, fracture, flow bubbles, softness, association with other volcanic rocks and lack of crystal faces.

• A volcanic bomb is a mass of molten rock larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains making them extrusive igneous rocks. Volcanic bombs can be thrown many kilometres from an erupting vent, and often acquire aerodynamic shapes during their flight.

Safety Note: Rattlesnakes by Owen Martin, AFMS Safety Chair
Though seemingly rare, poisonous snakes annually bite 6.500 to 7,000Americans. Always take the following precautions:

1. Always assume snakes areactive. Do not relax your vigilon sunny winter days.
2. Do not make “solo” tripsacross snake country which is remote from habitations and frequently used roads.
3. When traversing brush or grassyterrain, use a “decoy” such as a level rod or a lath, alongside your legs. Walk heavily to create vibrations that can be felt bysnakes (a snake does not hear).
4. Walk away from the shaded sideof clumps and bushes when the weather is hot and sunny.
5. Step on logs and large rocks, instead of stepping over them and into unseen areas. The safest policy is to walk around such obstacles.
6. Do not jump down from overhangs onto areas wheresnakes might be hidden from view.
7. Avoid steep climbs if possible where a snake, uphill from you, could strike the upper portions of your body. Bites on the torso, theneck, and the head are much moredamaging and more difficult to treat then those on the limbs.
8. Never climb vertical or near vertical faces where handholds on unseen areas above your head arerequired.
9. Do not attempt, under anycircumstances, to capture snakes!!
10.  Do not try to kill a snake unless itis a positive threat to safety.
11. Avoid likely snake areas such as small rodent trails, pack rats’ nests or gopher tortoise dens.
12. When necessary to move low-lying logs, large rocks and boards, use a pry bar, not your hands.
13. Double your precautions at night, especially in warm weather.
14. Keep vehicles near your work area for rapid transport if snakebite should occur.
15. If at all possible, maintain radio contact with isolated employees.
16. Know the location of the nearest medical facility where anti-venom is available and the quickest route there.
17. Do not collect rattles. A fine and highly abrasive dust often accumulates inside therattles and can cause lasting damage to the eyes.
18. Wear high leather boots or snake-leggings in high-hazard areas.
19. Remember that rattlesnakes do not always signal their presence by rattling.

Safety Note: Hazardous Materials (in progress)
Minerals with copper can be hazardous
Safety Note: Using Machinery Safely (in progress)
Procedures

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