Garnet from East Ongul Island in the Antarctic Region

Abstract

The sample was collected by Prof. Torii of Chiba University. Its colour is reddish brown and translucent and it forms a somewhat elongated crystal. It shows a few cracks and is brittle. Observed under the microscope, the greater part of the thin sections is quite homogeneous, but the bottom part of the crystal contains very small amount of hornblende, limonite and albite. We select its homogeneous part for our study. The following result were obtained: S.G. 3.954±0.005 a_0 11.530 Å (lattice constant) nNa 1.778±0.002 Si0_2 40.02% Al_20_3 21.90 Fe_20_3 1.53 FeO 21.34 CaO 5.20 MgO 8.94 K_20 0.01 Na_20 0.06 H_20^- 0.18 H_20^+ - Ti0_2 0.06 P_20_5 0.00 MnO 0.93 SrO 0.00 Total 100.17% F 0.002% Less 0 for F: 0.001% Rb and Li were detected by spectrochemical analysis, but Cr was not detected and, therefore, uvarovite-component is absent. Other rarer elements were not found. From the result of chemical analysis the authors studied its garnet-components and obtained the following results: Almandite 47.64% Andradite 4.59% Pyrope 35.49% Grossularite 10.10% Spessartite 2.18% By Boeke's classification this constitution belongs to pyralspite.