Compatibility diagram

These lines generally divide the diagram into subtriangles since, in accordance with Gibb's phase rule, a system of three components will contain three phases except at the degenerate compositions represented by the points and lines.

These are the compatible phases for the composition at the temperature and pressure (and, sometimes, degree of water saturation) for which the diagram is prepared.

If the rock is assumed to be saturated with quartz and carbon dioxide (though not depicted in the diagram), then at elevated temperature (granulite facies), the corner phases are calcite, sillimanite, and orthopyroxene.

The side of the diagram between calcite and sillimanite has a point added for anorthite (calcium feldspar), corresponding to an equal mixture (by mole percentage) of the two components.

Its components are: This diagram is less useful, because magnesium does not freely substitute for ferrous iron in many metamorphic minerals important in aluminium-rich rock.

ACF compatibility diagrams (aluminium-calcium-iron) showing phase equilibria in metamorphic mafic rocks at different P-T circumstances ( metamorphic facies ). Dots represent mineral phases, thin grey lines are equilibria between two phases. Mineral abbreviations: act = actinolite ; cc = calcite ; chl = chlorite ; di = diopside ; ep = epidote ; glau = glaucophane ; gt = garnet ; hbl = hornblende ; ky = kyanite ; law = lawsonite ; plag = plagioclase ; om = omphacite ; opx = orthopyroxene ; zo = zoisite
ACF compatibility diagram depicting compatible phases of the granulite facies. Cc=calcite; Sil=sillimanite; OPC=orthopyroxene; CPX=clinopyroxene; An=anorthite; G=garnet
ACFQ compatibility diagram for granulite facies. Symbols in addition to those of the previous diagram are Q= SiO 2 , q=quartz, cor=corundum, pc=periclase. Most silica-undersaturated phases, such as olivine or spinel , have been omitted. The previous diagram is the projection of the silica-rich corner of this diagram onto the ACF face.