The chromite bodies in the Tari District are embedded in ultrabasic rock. The writer has examined forty seven chromite samples from the region. The chromite is regarded as a solid solution of spinel, magnesiochromite, ferrochromite and magnetite, and its ideal formula is given as (Fe
a, Mg
b, Mn
c) (Cr
l, Al
m, Fe
n)
2O
4. The fact that the calculated lattice parameters of a few samples are higher beyond the error than the measured one may be caused by γ-Al
2O
3 and γ-Fe
2O
3 (maghemite) included as solid solution in the chromites. The formula for a solid solution which contains γ-Al
2O
3 and γ-Fe
2O
3 would be writen as (Fe
2a, Mg
2b, Mn
2c, Al
3u, Fe
3d-u, _??_
d/2) (Cr
3l, Al
3p+v, Fe
3q+3d/2-v)
2O
4, where u=2v/3, and m+n=p+q+2d. The difference of calculated and measured lattice parameters may be expressed as (0.206X+0.059Y)/100, and the difference of measured and calculated densities may be described by (0.11X-0.32Y)/100, where X and Y are molecular percentages of γ-Al
2O
3 and γ-Fe
2O
3 respectively. The chemical formula of the sample No. 36 from Wakamatsu Mine in the Tari District is denoted as follows. (Fe
20.196, Mg
20.770, Mn
20.0002, Al
30.016, Fe
30.004, _??_
0.013) (Cr
30.500, Al
30.388+0.027, Fe
30.030+0.005)
2O
4.
View full abstract