In the Yagoshi mine, a small lenticular mass of garnet rock is found in beerbachite which was formed from the sediments of tuffaceous rock by the contact action of dioritic magma. The garnet rock consists essentially of garnet with a small quantity of hedenbergite. The refractive index of the garnet is 1.824 and its cell constant is 11.907A. The content of MnO measured by a quantitative method is 0.17%. The refractive indices of hedenbergite measured on (110) are a'=1.726 and γ'=1.747 ; and 2V=(+)61°, c∧Z=41° ?? 43°. The chemical composition of garnet can be estimated, from the refractive index, the cell-dimension and the MnO content given above, as follows ; Gr=30 ?? 40%, And=50 ?? 60%, Alm=0 ?? 10%, Py=0 ?? 10% and Sp=0.38%. The present studies were carried out under the guidance of Prof. S. Kôzu, to whom the auther ?? s hearty thanks are due.

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