Igneous Rocks
Extrusive Rocks (rocks that cooled outside the earth)
Pumice	Appearance: light volcano rock, filled with air. Often white, but it doesn't have to be.
Basalt	Appearance: heavy, dense volcano rock. Often black, but not a requirement.
Obsidian	Appearance: glassy. It breaks in semi-circular patterns, just like glass. Shown black, obsidian may be any color.
Intrusive Rocks (rocks that cooled inside the earth)
Granite	Appearance: speckles. Crystals form in this rock, and distinct colors are seen.