A crystal face is a planar surface formed by breaking of a mineral crystal along a pre-existing plane of weakness. Mantle convection and gravitational sliding have both been proposed as causes of plate motion. Covalent bonds develop because of the uneven distribution of electrons around a compound and the fact the negative portion of the molecule is attracted to the positive portion of another molecule. Pegmatite is a very coarse-grained igneous rock made up mostly of feldspar and quartz. In the Bowen's reaction series, felsic magmas crystallize earlier than mafic magmas.
Mafic volcanoes are usually much more explosive than felsic volcanoes.
Ash flows are usually associated with felsic volcanoes, not mafic volcanoes. Quartz and potassium feldspar are excellent examples of metamorphic index minerals because they are only found in high grade metamorphic rocks. The crust, mantle, and inner core are all solid, but the outer core is liquid. Absolute geologic time is measured in terms of years, whereas relative geologic time is measured in terms of the relative ordering of events. The Neptunists thought that igneous rocks precipitated out of sea water, similar to the way sugar will precipitate out of sugar water if the solution is left to evaporate.