magma		When lava cools so quickly that no crystal structure develops.
texture		Igneous rocks that have a high silicate content
obsidian		Heated obsidian, used in gardening
felsic		The Latin word for "fire"
coarse grained		A black glassy igneous rock used by ancients to make sharp tools.
perlite		One use for granite, these are made from granite.
lava		Igneous rocks high in iron
pumice		What we call igneous rocks formed from cooling lava.
cobblestones		A mixture of minerals and possibly other materials
rhyolite		Melted rock found above the earth's crust
intrusive		Type of texture that extrusive rocks have.
glassy		The most abundant intrusive rock on earth.
mafic		Melted rock found beneath the ground
extrusive		One of three ways to classify igneous rocks
origin		One of three ways to classify igneous rocks
rock		Type of textrue found in granite.
fine grained		One of three ways to classify igneous rocks
ignis		A mafic rock produced when lava erupts on the ocean floor.
basalt		What we call igneous rocks formed from cooling magma.
composition		A low density extusive rock used as an abrasive
granite		A fine grained extrusive rock with a mineral composition similar to granite.