Tremolite Marble sample
Glaucophane Schist

Metamorphosed Carbonate Silicate Rock Information


Metamorphism of a pure calcite limestone can produce a beautiful white calcite marble that is great for statues but does not provide much information about its metamorphic P-T path. However, metamorphosed dolomite with some quartz sand mixed in may have a variety of Ca-Mg-Si minerals that offer evidence regarding the conditions of metamorphism in a chemically tractable system. H2O must be added to produce some of the minerals and CO2 is released in carbonate-consuming reactions.

Mineralogy of Metamorphosed Carbonate Silicate Rocks

Minerals List

Metamorphosed CarbSi Rock Minerals. Click on the image to visit the list of minerals and links to their properties.

Calcite and dolomite are the carbonate minerals most likely to occur in metamorphosed carbonate silicate rocks. Calite and dolomite will look very similar in thin section, so some petrographers stain the calcite in their carbonate-bearing thin sections with Alizerin Red S. If the protolith is dolomitic limestone with quartz sand, the metamorphic silicate minerals that most commonly occur are talc, tremolite, diopside, forsterite, and wollastonite. If no Fe is present, these minerals are all colorless. A small amount of iron will add some green color to these minerals in hand sample, although more iron is needed to make them colored in thin section than in hand sample. If some mud is also in the protolith, Al-bearing minerals may be present such as phlogopite, clinzoisite, and plagioclase. A list of minerals commonly observed in metamorphosed carbonate silicate rocks and links to the properties of these minerals can be found here.

Samples of Metamorphosed Carbonate Silicate Rocks

Eclogite Thin Section

Diopside-Wollasontite-Grossular Calc-silicate Rock. A sample of metamorphosed carbonate silicate rock. Click on the image to see a list of metmorphosed carbonate silicate rock images in the Rock Library, including this sample.

The Rock Library includes images of hand samples and thin sections of metamorphosed carbonate silicate rocks. The IUGS recommends that rocks >95% carbonate minerals be called pure marbles, rocks with 50% to 95% carbonate minerals be called impure marbles, rocks with 5% to 50% carbonate minerals be called carbonate-silicate rocks, and those with <5% carbonate be called calc-silicate rocks. Links to images of metamorphosed carbonate silicate rocks can be found on this list.

SCM Diagram

The mineral assemblages and chemical reactions of metamorphosed siliceous dolomite rocks can be represented nicely on an SiO2-CaO-MgO (SCM) diagram.
Minerals List

SCM Diagram . Click on the image to show compositions of metamorphosed carbonate silicate rock minerals or to plot bulk compositions, both on an SCM diagram.

This diagram assumes that the volatiles H2O and CO2 are free to come and go and is a projection from those oxides. You can plot bulk rock compositions from your own chemical data (upload a .csv file) on an SCM diagram by clicking here. By clicking buttons on the linked SCM diagram you can see where the compositions of common minerals plot on the diagram.

Chemical Reactions in Metamorphosed Carbonate Silicate Rocks

Chemical reactions among carbonate and silicate minerals may consume from or yield to the metamorphic fluid H2O and/or CO2. This means that equilibrium mineral assemblages of metamorphosed carbonate silicate rocks depend on the mole fraction XCO2 [= CO2/(CO2 + H2O)] in
Minerals List

Reactions and Assemblages . Click on the image to see a T-P diagram with chemical reactions and generalized SCM mineral assemblages for metamorphosed carbonate silicate rocks as a function of temperature, pressure, and XCO2.

the fluid as well as on temperature, pressure, and bulk composition. You can see this by clicking on the T-XCO2 diagram on the right. When the diagram opens, you will see unvariant reaction curves. Click on the "Show Assemblages" button and mouse over the T-XCO2 graph to see the mineral assmblages that are stable between reactions. Then click on the "Change Pressure" button and use the slider to see how the reactions change with pressure.