LL Demos & Labs: Rock Profile: Obsidian Family
This specimen comes from Southern Utah, near Beaver. Obsidian is formed from rhyolitic lava which contains a lot of silica, the material used to make glass. Because rhyolite is a thick, sticky kind of lava, it oozed from the ground slowly. The black color is produced by the presence of iron. This color is spread unevenly throughout the lava. If you hold your sample up to a bright light, you’ll see some dark areas and other areas that are almost clear. If your sample has white spots through out the black rock, and is named snowflake obsidian or sometime flowering obsidian. The white spots are mineral impurities made of cristobalite.