Page 60 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-11.3 S O L I D S

IR-11.2.2 Mineral names
Mineral n ames should b e u sed only to designate actual minerals and not to define chemical
composition. Thus, the name calcite refers to a p articular m ineral (contrasted with other
minerals of similar composition) and is not a t erm for the chemical compound the
composition of which is properly expressed b y t he name c alcium carbonate.
A m ineral name m ay, however, b e u sed to indicate the structure type. Where possible,
a n ame t hat refers to a g eneral group should r eplace a m ore specific name. For example,
large numbers of minerals have been named that are all spinels, b ut which have widely
differing atomic c onstituents. In this c ase, the generic name ‘spinel type’ s hould b e u sed
rather than the more specific names chromite, magnetite, etc. T he generic mineral name,
printed i n i talics, should be accompanied by a r epresentative chemical formula. This is
particularly important for zeolite types. 5

Examples:
1. FeCr 2 O 4 (spinel type)

2. BaTiO 3 ( perovskite type)

IR-11.3 C H E M I C A L C O M P O S I T I O N

IR-11.3.1 Approximate formulae

The formula used in any given c ase depends u pon how m uch information is to be conveyed.
A g eneral notation, which can be used even when t he mechanism of the variation in compo-
sition is unknown, is to put the sign , (read as circa, o r ‘ approximately’) before t he
formula.

Examples:

1. ,FeS
2. ,CuZn

If it is desirable to give more information, one of the notations described below m ay be used.

IR-11.3.2 Phases with variable composition
For a p hase where the variation in composition i s c aused s olely or partially by isovalent
substitution, the symbols of the atoms or groups that replace each other may be separated by
a c omma and placed together b etween p arentheses. If possible, the formula is written so that
the limits of the homogeneity range, w hen o ne or the other of the two a toms or groups is
lacking, a re represented.

Examples:

1. (Cu,Ni) denotes the complete range of compositions from pure Cu to pure Ni.
2. K(Br,Cl) comprises the range from pure KBr to pure KCl.

Phases for which substitution also r esults in vacant p ositions are denoted in the same way.

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