Names of solid phases

Names for stoichiometric phases, such as NaCl, are derived simply as in Chapter IR-5, whereas formulae are derived as presented in Chapter IR-4. Although NaCl in the solid state consists of an infinite network of units, (NaCl)oo, the compound is named sodium chloride and represented symbolically as NaCl. 

However, for non-stoichiometric phases and solid solutions, formulae are preferable to names, since strictly systematic names tend to be inconveniently cumbersome. They should be used only when unavoidable (e.g. for indexing) and should be constructed in the following style. 

1 Approximate formulae The formula used in any given case depends upon how much information is to be conveyed. A general notation, which can be used even when the mechanism of the variation in composition is unknown, is to put the sign (read as circa, or approximately ) before the formula. Examples 1. FeS 2. —CuZn If it is desirable to give more information, one of the notations described below may be used. 

Mg)Cl2 denotes a solid mixture intermediate in composition between LiCl and MgCl2. 

Mg3)Al6012 represents a solid mixture intermediate in composition between MgAl204 ( = Mg3Al6012) and A1203 (spinel type) ( = Al2Al60i2). 

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IR-11.1.2 Stoichiometric and non-stoichiometric phases IR-11.2 Names of solid phases IR-11.2.1 General IR-11.2.2 Mineral names IR-11.3 Chemical composition IR-11.3.1 Approximate formulae IR-11.3.2 Phases with variable composition IR-11.4 Point defect (Kroger-Vink) notation IR-11.4.1 General... 

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