ON THE CHEMICAL COMPOSITION OF GERMANITE

Svetlana N. Nenasheva

Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, sn@fmm.ru

Germanite is a very rare mineral that commonly occurs as small segregations in association with bornite, renierite, fahlores, sphalerite, galena, and other sulfides and sulfosalts. Very fine structures of replacement of germanite for renierite are often observed. Such small segregations are difficult to study. Optical properties of germanite are slightly variable in different areas and in samples from different deposits. The chemical composition (concentrations of the principal elements) of germanite varies over a wide range. In addition, the mineral was revealed to contain a wide set of admixtures. Therefore, different researchers propose different formulas for germanite. Chemical and electron microprobe analyses of germanite, accessible in literature, were compiled by the author, and peculiarities of the chemical composition of germanite were studied. It has been revealed that 28 analyses from 37 ones are adequately recalculated to the formula with 66 atoms in the unit cell; 6 analyses, to the formula with 64 atoms; and 3 analyses, with 68 atoms. The Me/S ratio in the analyses varies from 32:32 to 34:32 and to 36:32; that is, this ratio in the real analyses is inconstant. This fact suggests that we deal either with solid solutions or with three different, but similar in the chemical composition and properties, minerals. The second assumption is more probable. It is concluded that there exist three mineral species close to germanite in the chemical composition.

8 tables, 3 figures and 22 references