QUESTION #5. a) What is the valence state of Fe in the minerals shown on this tr

Question

QUESTION #5. a) What is the valence state of Fe in the minerals shown on this triangle? b) Where on this diagram would you plot a carbonate with the composition: Cal.osMgo7Fe0.2s(C03)2, and what name would you give this mineral? CaCO3 calcite c) According to this diagram, what ionic substitutions occur among these carbonates? Are they examples of isomorphous or coupled substitutions? CaMg(CO3)2 dolomite CaFe(CO3)2 ankerite d) What pair of minerals exhibits complete solid solution on this diagram? MgCO3 magnesite e) Name a pair of minerals exhibiting FeCO3 partial solid solution on this diagram? siderite molecular % f) If the mineralogy of a specimen of overall composition of Cao.1sMao.3sSio.s is described by the tie-lines on this diagram, what minerals (name, composition) should be present in the specimen?

Explanation / Answer

a, The valece state of Fe in the minerals in the diagram is 2 i.e. Fe is in the ferrous state.

b Ca1.05Mg0.7Fe0.25(CO3)2 is plotted in the middle of the diagram, i.e. mid way between dolomite and ankerite. Its name is Iron-rich Dolomite

c. In the diagram, ionic substitution occurs between Fe2+ and Mg2+. Coupled substitution occurs as the overall charge remains constant.

d. Complete solid sokution can be seen between magnesite and siderite.

e. Partial solid solution can be seen between calcite and dolomite

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