Obsidian
Rock made of volcanic glass
Common · Variable (silica-rich volcanic glass)
Volcanic glass formed when silica-rich lava cools too rapidly for crystals to grow. It breaks with a conchoidal fracture whose edges are sharp enough to cut flesh. Used for blades and tools for thousands of years.
Rock
- Kind of rock
- Volcanic igneous rock
- Rock family
- Volcanic rock
- Texture
- glassy
- How it forms
- Silica-rich lava, usually rhyolitic, cools too fast for crystals to grow.
- Uses
- Blades and tools since prehistory; obsidian scalpels have been tried in surgery.
Identity
- Formula
- Variable (silica-rich volcanic glass)
- Chemical class
- Silicate
- Also known as
- Volcanic glass, Dragon glass (folklore)
- Used in alchemy
- Obsidian Powder
Crystallography
- Crystal system
- Amorphous
- Habits
- Massive, Nodular
- Fracture
- Conchoidal
Physical properties
- Mohs hardness
- 5.5
- Density
- 2.35 g/cm³
- Luster
- Vitreous
- Colors
- black, brownish-black, dark green, red, multicolored
- Streak
- white
- Transparency
- Opaque, Translucent
Geology
- Origins
- Volcanic
- Host rocks
- Volcanic rock
- Associated minerals
- cristobalite, Magnetite
- Geography
- Iceland, Mexico, USA (Oregon, Wyoming), Japan, Turkey
Classification
- Rarity
- Common
- Gem quality
- No
Arcane properties
- Affinity
- Shadow, Death
- Effects
- Warding, Necromancy
- Planar origin
- Material Plane
Sources
- Obsidian. Mindat.org (Hudson Institute of Mineralogy).
- Obsidian. Gemdat.org (Hudson Institute of Mineralogy).
- Rhyolite. Wikipedia.
- M. R. Gillespie, M. T. Styles, BGS Rock Classification Scheme, Volume 1: Classification of igneous rocks (Research Report RR 99-06). British Geological Survey, 1999.
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