Crystal Chemical Classification of Minerals by A. S. Povarennykh

By A. S. Povarennykh

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V gives only a general indication of the degree of closure of a coordination polyhedron, and it does not provide an indication of bond strength sufficiently accurate for the purposes of comparison. The a of (ll) (Table 6) allow this comparison; the range for oxygen coordination is very great. 12 (NO a) , or by a factor greater than 400. The cation a for any compound readily enables one to determine the bond homogeneity (isodesmic or anisodesmic). 7. The anisodesmicity factor A = a max / a min gives us the following scheme for the classification of minerals: 1) isodesmic (A of 1-3); 2) slightly anisodesmic (A of 3-8); 3) moderately anisodesmic (A of 8-20); 4) stronglyanisodesmic (A of 20-50); and 5) very strongly anisodesmic (A> 50).

Natural crystalline bodies) GASES 8 \ / 1-3'~ B This shows why Vernadskii often stressed the difficulty of formulating a strict definition of a mineral. " As regards a classification, which he did not give in respect of the geochemical approach to the definition of a mineral, he said (1908) [33) that "in the study of minerals these questions are largely open to personal views and preferences. " The subsequent history of mineralogical classification has not confirmed these statements of his, and he himself later largely abandoned them (Vernadskii and Kurbatov, 1937 [94]1.

A V of one (when the bond order in cation-oxygen polyhedra is 2) gives completely closed configurations or typical molecular compounds not having outward-directed valence bonds and which are held together only by residual (van der Waals) forces. , diamond, Si0 2, and BFa). V gives only a general indication of the degree of closure of a coordination polyhedron, and it does not provide an indication of bond strength sufficiently accurate for the purposes of comparison. The a of (ll) (Table 6) allow this comparison; the range for oxygen coordination is very great.

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