The first results of studies of the distorted shape of dodecahedral diamond crystals from placers of the Yakutian diamond-bearing province
A new method of computer analysis of the symmetry of the real shape of diamond crystals of dodecahedral habit is tested. Produced the first objective data on the distorted form of crystals from mineral deposits of the Yakutian diamondiferous province: placer Kholomolokh, Anabar diamondiferous district, Pyropovy Ruchey placer Daldyno-Alakit diamondiferous district. The principal possibility of analyzing the symmetry of the real shape of rounded diamond dodecahedroids with the help of reliable instrumental measurements of crystals is shown. Compared with dodecahedrons kimberlite origin from the deposits of Pyropovy Ruchey, dodecahedron placer Kholomolokh (representing placers of the northeastern Siberian platform) have a significant degree of curvature of the convex faces of dodecahedron, which requires amendments to results of measurement of distances between parallel faces. The discrepancy of the measurement results between the curved faces of dodecahedral crystals of kimberlite origin is within the measurement error of the device and does not require correction. The crystals from the deposits of Pyropovy Ruchey were 7, and placer Kholomolokh 13 morphological types of distortion of the rhombic dodecahedron. Common morphological types of distorted rhombododecahedron are varieties №2 [0363], №5 [0444], №7 [0444], №8 [0462] with matching face sets. The external symmetry of crystals mostly corresponds to the lower categories of point symmetry groups. For the first time, the external pseudotrigonal symmetry of group 32 was observed in diamond dodecahedroids. This symmetry found in crystals from placers Kholomolokh.