Obsidian is perhaps best known in its role as the dark black blade atop ancient spears ... origin is what classes rainbow obsidian as an igneous rock. Lava destined to become obsidian cools ...

Igneous rocks close igneous rockIgneous rocks are those ... which originates from clay. Slate is dark grey/green in colour and can be split into thin layers for use as roofing material.

Shining diamonds speckle the dark, igneous rock that lines the pipe, and the diamonds themselves contain tiny bits of other minerals from hundreds of miles beneath Earth’s surface. Within one of ...