铬尖晶石的晶胞参数与成因特征

铬尖晶石成分与晶胞、比重的关系1955年米赫耶夫提出尖晶石类总的晶胞公式为: (单位kx) 两价平均离子半径 三价平均离子半径。

UNIT CELL CONSTANT AND GENETIC CHARACTER OF CHROME SPINELS

The unit cell constant (a), specific gravity (G), reflectivity (R), microhardness (H) and chemical composition of thirty chrome spinel samples from deposits of different genesis in China were determined. On the basis of crystallo-chemical properties, a new formula of unit cell constant for chrome spinels is proposed: a = 8.367 A-0.01745 (Al+3)A, where (Al+3) is the number of Al+3 in the unit cell. It is more accurate than Mikheev’s formula. The composition of chrome spinel could be calculated directly from its unit cell constant by the formula: (Al+3) =479.45-57.3.a. Based upon the theoretical calculation, a new curve showing the relation between sp. gr. and composition is plotted. From the above relationship it is easy from a and G to derive the crystal chemical formula: R8+2 (Mg+2, Fe+2) R16+3 (Al+3, Cr+3 4- Fe+3) O32. A tetragonal composition diagram Mg+2-Fe+2-Al+3-(Cr+3+Fe+3)of chrome spinels constructed from a and G is also given. It is clearly shown that the chrome spinel of geosynclinal type (Alpine type) is quite different from that of platform type (or stratiform type). A simplified classification method for chrome hpinel groups is proposed. "Molecular Iron Content FCr" is probably an important factor of metallogenetic process and can be used as an indicator for the enrichment of chromite ore. Finally, some mineralogical characters of the chrome spinels associated with platinum diposits are discussed.