鳥取県多里地方産のクロム鉄鉱に関する研究

鳥取県多里地方のクロム鉄鉱およびそれに関連する二，三の論文を主に日本岩石鉱物鉱床学会誌と島根大学論集に発表してきた。この論文には，更にクロム鉄鉱について主に記載するが，それに附随する岩石類に関しても若干述べることにする。
In the present paper, the writer mainly described the results of the mineralogical studies on the chromites of the chromite bodies of the Ogiri and 34 m. levels of Hirose mine, and the bodies of the 7th, South and Chugiri levels of Wakamatsu mine, for these bodies have been worked.
Serpentinite was intruded into Palaeozoic formation and invaded by granitic rock in the region. It seems that gabbroic rocks are differential dykes from an ultra-basic magma rather than xenoliths by his detailed survies the occurrence of the rocks.
Chromites splitted at early stage in deep zone from an ultra-basic magma are assumed to had been intruded metasomatically in pre-solidified ultra-basic rocks.
Chromites at the central parts of the chromite bodies of the above mentioned levels are not almost altered or very nearly altered, and are low in magnetite and high in spinel components. Chromites at the marginal portions of the chromite bodies are considerably altered, and generally high in magnetite component. It is considered that the black margins and cross cutting lines of the chromites were formed from deuteric concentration of iron oxide generated by high pressure of such magmatic emanation as water vapour existing during crystallization. Sometimes, these increase suddenly towards the surface of the chromite bodies until the mineral is almost replaced. Chromites on the edges or as veins of the bodies are not nearly altered, and comparatively low in magnetite component. It seems that the chromites in the said region, were not altered by late hydrothermal water that altered olivine or enstatite to serpentine or chlorite.
The refractive indices of the chromites that were not altered, represent the idices of the chromites, but the indices of altered chromites express the traslucent parts of the ones, as the indices of the black opaque parts can not determined by the immersion methord.
The atomic planes of the chromites determined by X-ray powder methord are 220, 311, 400, 511 or 333, 440, 622, 444, 731 or 553, 800, 662, 840, 931, 844. The lattice parameters range from 8.188 to 8.244 Å for 25 chromite samples in the region. The lattice parameters are principally controlled by Cr_2O_3 and FeO + (Fe_2O_3) contents, the large parameters being due to increase of Cr_2O_3 and FeO + (Fe_2O_3) contents in the chromites.