OBSIDIAN
...
naturally-occurring volcanic glass.
Pure obsidian is usually
dark in appearance, although the colour varies depending
on the presence of impurities. Iron and magnesium
typically give the obsidian a dark green to brown to
black colour. A very few samples are nearly clear. 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 obsidian) or rainbow
sheen (rainbow obsidian).
Glass Mountain, a large
obsidian flow at Medicine
Lake Volcano.
Each
individual piece is Exclusive |
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