Definition
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth
Arkose is a sedimentary rock, specifically a type of sandstone containing at least 25% feldspar
History
Origin
Ethiopia
France
Discoverer
Obsius
Alexandre Brongniart
Etymology
From Latin obsidianus, misprint of Obsianus (lapis) (stone) of Obsius
From Auvergne region of France used by a French geologist Alexandre Brongniart in 1826 who applied this term to some feldspathic sandstones
Class
Igneous Rocks
Sedimentary Rocks
Sub-Class
Durable Rock, Medium Hardness Rock
Durable Rock, Hard Rock
Family
Group
Volcanic
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Other Categories
Opaque Rock
Coarse Grained Rock, Opaque Rock