A study of moissanites in the serpentinite from south Dabie Mountain

Moissanites were found in serpentinites from Tinziling, Gushan and Huxi areas in south Dabie Mountain. The sizes of grains are mainly 0.02~0.08mm and subordinately 0.1~0.17mm. The crystals are uniaxial (+) and biaxial (+), 2V=370° with the biaxial crystals being dominant, showing obvious biaxiality.The Raman shifts of moissanites in the section are stable:a primary peak of 788~789cm^-1, a secondary peak of 986~972cm^-1, and a weak peak of 767~784cm^-1. The mixture of Al, O in moissanites may cause change in texture of moissanites, and even cause comparatively larger deviation in Raman spectral analysis: a primary peak of 776.85cm^-1, and a secondary peak of 964.82cm^-1. The energy spectral analysis shows that the moissanites were mixed with a lot of other elements, such as O, Fe, Ca, K, Ni, Ti, S, Cl and Na. All of these elements may affect its texture. It is also shown that at the early stage it crystallized at relatively high temperature and had relatively abundant mixed elements. Besides, there exist fluid inclusions in moissanates, whose components include CH₄, C₂H₆, C₃H₈, C₆H₆, H₂O, etc. The moissanite-bearing serpentinite is a continent mantle rock; when it intruded upward, the biaxial crystal of moissanite was formed under the condition of high temperature and different stresses. According to experimental data, SiC was formed at the temperature >1600℃ and under the pressure≥6.0GPa. Therefore the moissanites here should have been produced under extremely low reduction condition, situated in asthenosphere of the upper mantle or the lower earth crust.