Obsidian

Obsidian

Obsidian is an igneous rock composed mainly of glass (silicon dioxide). Usually, it is a shiny black rock that has noticeable bands. This rock forms when silica-rich magma cools very quickly. Minerals associated with obsidian include quartz and feldspar. Obsidian can be found in Japan and Yellowstone Park, USA. It was used in ancient times for weapons and tools. [LM] {CC} {SS}