Obsidian
- John Seach
Obsidian is
dense volcanic glass, usually rhyolite in composition and typically black
in color.
Obsidian is
often formed in rhyolite lava flows where the lava cools so fast that crystals
do not have time to grow.
Black color
of obsidian results chiefly from magnetite, Fe304.
Obsidian
www.volcanolive.com
Copyright John Seach