Whether the origin of rock may be magmatic, sedimentary, or metamorphic, there are certain basic processes by which the rocks and the minerals that make them up are formed. The most important of these are crystallization from molten material, sublimation, or crystallization directly from a gas to solid, formation from water solutions, and weathering.

The kinds of minerals and rock mixtures that form depend in large part on the conditions under which they form. Because of this there is an all important law governing the entire event. At the time of its formation, a mineral must be in equilibrium with its environment. This means that if pressures or other conditions change, then the kinds of materials forming may also change. Even if the minerals have already formed before the change in growing conditions, they will still change in composition and structure. To exist in the end, the mineral must be perfectly adjusted to or at least in satisfactory agreement with its surroundings.