鳥取県多里地方産のクロム鉄鉱の化学組成ならびにその屈析率,格子恒数との関係

筆者はサキに広瀬鉱山と若松鉱山との附近の地質および両鉱山の各鉱床について述べた。47個のクロム鉄鉱の肉眼的，顕微鏡的特徴を記載し、それらの化学組成についても表示し，更にクロム鉄鉱の屈折率，格子恒数についても記述した。

The chromite deposits in the Tari district are the differentiation products of the ultrabasic magma and lenticular or massive. They extend nearly parallel to the longer axis of serpentinite. The ore is now taken from the Ogiri and the 34-m levels of Hirose mine and No. 7, Minami, and Chugiri levels of Wakamatsu mine. Generally massive ore prevails in the inner portion and porphyritic one in the outer portion. The chromium content of 47 sample of the ore from the district is low, ranging from 31.22 to 41,33% Cr_2O_3. The norms of the inner portion of the ore body except the portion metamorphosed by gabbro, the outer portion, and edge are as follows :
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Inner portion Outer Portion Edge
Spinel (MgAl_2O_4) 53.8 - 58.5 38.7 - 59.4 52.5 - 57.5
Chromite (Mg,Fe) Cr_2O_4 39.3 - 43.1 36.9 - 53.2 40.6 - 44.4
Magnetite (FeFe_2O_4) 1.3 - 3.1 2.5 - 9.4 1.9 - 4.4
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It is ascertained that the inner portion is the highest in the spinel composition and the lowest in the magnetite composition, that the edge is high in the spinel composition and low in magnetite composition, and that the outer portion is low in the spinel composition and high in the magnetite composition.
As the triangular diagram representing norm shows the chromite in the district belongs to chromian spinel, which is rare in Japan as well as in foreign countries.
The thin section of the chromite from the inner portion and the edge is mostly yellow to orange, while the chromite in the outer portion having been metamorphosed the thin section is usually black.
The ratio Cr/Fe of the chromite in the district is 1.7-3.6. It is generally greatest in the inner portion and smallest in the outer portion. The ratio Mg/Fe is 0.7-1.8. In the chromite whose Cr_2O_3 content is not very variable the ratio Mg/Fe is controlled by the quantity of Al_2O_3.
The index of refraction of the chromite in question is 1.86-1.89 and the color of the thin section of the chromite is yellow to light red, inclining to red with increase of the index.
The net plane indices of the chromite are 220, 311, 400, 511 or 333, 440, 622, 444, 731 or 551, 800, 662, 840, 931, and 844. The lattice constant a_0 =8.188 - 8.224Å and it becomes greater in proportion to the quantity of Cr_2O_3 and Feo + Fe_2O_3. The lattice constant of the sample shown in the triangular diagram for the norm of spinel group is approximately the same with the measured number like the index of refraction when MgCr_2O_4 and FeCr_2O4 do not greatly differ.