Calcite chemical formula

The listed chemical formulae are ideal and most of these minerals contain trace and minor elements which undoubtedly affect the CL. Several of these minerals have polymorphic or compositional varieties which also may, or do, show CL (e.g. the silica polymorphs quartz, cristobalite, tridymite phosphate compositional varieties apatite, whitlockite, farringtonite, buchwaldite carbonate compositional varieties calcite, dolomite, magnesite). Glass and maskelynite (shock modified feldspar), although not strictly minerals, are relatively common. Below are described the CL observations for the most common phases including enstatite, feldspar and forsterite and they are related to their use for interpreting the mineralogy of meteorites. The observations for the other minerals are sporadic and many details have yet to be studied. 

Polymorphism occurs when different structures can occur for the same chemical formula. The atoms are the same but their atomic arrangement differs between the structures. Although ultimately thermodynamics (the minimum Gibbs free energy) dictates which of the probable structures is formed at a particular temperature and pressure, other factors such as electrostatic interaction mean that a variety of different structures is possible. Polymorphism applies not only to elements, e.g. black and red phosphorus, but also to compounds such as calcium carbonate, which can exist in a number of forms including calcite, aragonite and vaterite. 

Write chemical formulas for the following minerals (a) calcite, (b) dolomite, (c) fluorite, (d) halite, (e) corundum, (f) magnetite, (g) beryl, (h) galena, (i) epsomite, (j) anhydrite. 

There are also naturally occurring fibrous silicate minerals. The most commercially important of these today is Wollastonite. It has the chemical formula CaSiOj. Wollastonite particles are shown in Fig. 1.16. Asbestos, now largely banned as a health hazard, is also a fibrous silicate. Wollastonite is obtained by mining or reaction between calcite and silica at temperatures higher than 450 °C ... 

Formula Chemical class Chemical type (Ni,Mg,Fe)C03 (see notes) Crystal system Anhydrous normal carbonate Mineral group ACXOj) Space group Trigonal Calcite R3c... 

The first nomenclature for inorganic structure types has been proposed by Ewald Hermann in 1931. They used letters to designate the kind of chemical compound and numerals to distinguish among compounds with the same general formula. The chemical elements are designated by the letter A, the binary compounds by the letter B, the AB2 compounds by C and so on. Examples are A1 for Cu, A10 for Hg, B1 for NaCI, B3 for ZnS (sphalerite), HI2 for Mg2Si04 (olivine), G1 for CaCOa (calcite). This notation has not received much acceptance, possibly due to its lack of self explanatory structural information. 

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