Rock Classification

Rocks that have solidified from a molten state.  There are two types of Igneous rocks: 
Plutonic - Rock from magma rising up from deep under the earth's crust, and solidifies as it cools before it reaches the earth's surface.
Volcanic - Rock that was originally lava, hot magma that reached the surface of the earth before it hardened.
examples of: 
plutonic igneous rocks - Granite, Peridotite
volcanic igneous rocks - Obsidian, Basalt, Rhyolite
Rock formed by the accumulation of particles on or near the earth's surface, and compacted down, often under extreme pressure, creating rock layers. examples of sedimentary rock: 
Limestone, Shale, Sandstone, Dolomite, Gypsum, Quartzite, and stones containing fossils
rocks resulting from changes within preexisting rocks, by extreme pressure, temperature, and chemical activity. examples of metamorphic rock: 
Kyanite, Mica, Garnet, Calcite, Quartz, Pyrite, Marble, Gneiss, Schist