What is an ACF diagram?

ACF diagram A three-component, triangular graph used to show how metamorphic mineral assemblages vary as a function of rock composition within one metamorphic facies.

What is Chemographic diagram?

Minerals and rocks have chemical compositions that comprise some of the most important data for phase equilibria studies. Important relationships among rocks and minerals can be discovered or demonstrated by the construction of composition diagrams (also called chemographic diagrams) to display the data.

Why ACF diagrams are not suitable for rocks and mineral with Fe Mg solid solutions?

One of the problems associated with ACF and AKF diagrams is that Fe and Mg are assumed to substitute for one another and act as a single component. We know, however, that in natural minerals the composition of Fe – Mg solid solutions is very much dependent on temperature and pressure.

What is AFM diagram?

The AFM diagram is a ternary plot used to show the relative proportions of the oxides of alkalis (A), iron (F), and magnesium (M) in igneous rocks. The components of the diagram are thus A (Alkalis: Na2O + K2O), F (FeO & Fe203), and M (MgO).

What are AFM diagrams?

What is a Harker diagram?

Harker diagram (variation diagram) A diagram that shows the amount of each of the chemical constituents of a rock as a proportion of the main ingredient (usually silica).

What is Chemographic projection?

Chemographic projections are often used in metamorphic petrology to plot complex compositions on two-dimensional triangular diagrams. A popular chemographic projection for metapelites is the AFM diagram, which represents Al2O3, FeO, and MgO at its corners.

What is metamorphic phase rule?

Since metamorphism usually involves long periods of geologic time, most metamorphic rocks represent an equilibrium mineral assemblage. The Phase Rule for Metamorphism. Recall that the phase rule states that. F = C + 2 – P.

How do you identify staurolite in a thin section?

In thin sections staurolite is commonly twinned and shows lower first order birefringence similar to quartz, with the twinning displaying optical continuity. It can be identified in metamorphic rocks by its swiss cheese appearance (with poikilitic quartz) and often mantled porphyroblastic character.