| Themes > Science > Earth Sciences > Geology > Rocks and Minerals > Minerals & Rocks Additional Information > The most common igneous rocks > Obsidian |
Obsidian (pronounced: ob-sid-ian) Obsidian is formed when rhyolite magma is cooled rapidly, e.g. on lava surfaces and at contact surfaces of intrusions. It is jet black in color and has a glossy luster. Obsidian occurs in Hrafntinnuhraun at Tirfajökull. |
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