Si-bearing sakhaites from somemetasomatites of Eastern Siberia were investigated byIR spectroscopy, X-ray diffraction and microprobeanalyses. As a result there was proved the existanceof isomorphic series between sakhaite and harkeritewithin range from pure sakhaite to Si-deficientharkerite. Data on chemical composition and IR spectrasupport the existance of isomorphic substitution bythe Al[Si(O, OH)4]4 →4[BO3] scheme. Increase of Siand Al contents in a mineral is accompanied bymonotonous change of interplanar distances. There areindices of structural ordering in IR spectrum near theequimolar composition (sakhaite: harkerite = 1:1). Thepaper contains also the new description of karlite(the very first in Russia, the second in the wholeworld) which has been found in close association with sakhaite.
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