Crystal structure of olivine and its chemical bonds.

Abstract

Olivine with well-developed cleavages on (100), (010) and (001) crystal planes has been found in some dunite bodies in Japan and its mineralogical meaning has been discussed (Kuroda and Shimoda, 1967; 1969). Here, the foregoing crystal models and discussion are critically summarized and new crystal structure-model for the cleavable olivine is dresented (Table 1, column 6; Fig. 4), This model well explains the observed intensities of X-ray powder diffraction of the cleavable olivine. Considering the minute differences of crystal structure (structure factor) among olivines with various origins, the differences of observed intensities of x-ray powder diffraction of such olivine are also well explained. The minute change of crystal structure of olivine is considered from the nature of chemical bonds, especially between MgII and O (Figs. 7, 8). Under the condition of high pressure chemical bond may show more covalent character and under the condition of low pressure and high temperature it may show more ionic character. The nature of chemical bonds may not be complied quickly as contraction or expansion of volume with new P-T condition, so the dimension of unit cell is not so different. Consideration on the interatomic distances is well discussed and other crystal chemical problems on olvine are also discussed.