Conventions for naming polymorphs

Part of the difficulty encountered in searching and interpreting the literature on polymorphic behaviour of materials is due to the inconsistent labelling of polymorphs. In many cases, the inconsistency arises from lack of an accepted standard notation. However, often, and perhaps more important, it is due to the lack of various authors awareness of previous work or lack of attempts to reconcile their own work with earlier studies (see, for instance. Bar and Bernstein 1985). While many polymorphic minerals and inorganic compounds acmally have different names (e.g. calcite, aragonite and vaterite for calcium carbonate or rutile, brookite, and anatase for titanium dioxide) this has not been the practice for molecular crystals, which have been labelled with Arabic (1, 2, 3.) or Roman (I, II, III.) numerals, lower or upper case Latin (a, b, c. or A, B, C.) or lower case Greek a, P,y, ) letters, or by names descriptive of properties (red form, low-temperature polymorph, metastable modification, etc.). 

In view of the body of literature already extant and the questions surrounding the definition of a polymorph it does not appear to be practical to define hard and fast rules for labelling polymorphs. The Kofler method has clear advantages, since the melting point designation may eliminate some questions of identity hence its use should be 

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