Strong oppositely charged e: weak valence can migrate, weak chemical imbalance - graphite. Structure determines by positive ions (cations) or negative ions (anions) How a rock breaks cubic, rhombohedra, or basal. Extrusive when created at surface, intrusive when not. Formed by deposition or precipitation of weathers transported material - sediment. Formed by change of existing rock (meta + morph = to change form) Coarse grained (granite) abundant, associated with mountain building. Fine grained (rhyolite: most abundant made of calcite. Rocks w/ granular texture interlocking grains of granite: marble = metamorphic limestone/ quartzite = metamorphic sandstone. Schistosity platy minerals show a layers structure, referred to as schist, ie gneissic. Banded appearance pressure and heat - follated: rate of cooling (slow cooling allows crystals to grow larger) affect the crystal size and shape, gabbro (p) vs. basalt (a): same composition, different texture. Theory that the earth"s crust is a series of plates which move about the surface.