| Text Description: |
1906 lava? Medium dark-gray (N4) hypersthene basalt, porphyritic, with vesicular structure. Plagioclase phenocrysts range in size from 0.1 to 3 mm. The median composition is An[58?], but one rounded grain of anorthite (average index 1.58) was seen as presumed to be a xenocryst. The salite crystals have nY 1.70, suggesting a composition about Ca50Mg30Fe20. The hypersthene prisms, which range in size from 0.1 to 1 mm, have nZ 1.70 corresponding to En73Fs27. The optic axial angle of the olivine seen in thin section was the same as that in 46AC97, suggesting that here also its composition is about Fo72Fa28. Olivine is rare, and no olivine was found in the crushed fragments. The groundmass consists of plagioclase laths and augite rods in brown glass with an index of 1.50 plus/minus 0.005. The accessory minerals are magnetite or ilmenite, from 1 to 0.1 mm, and apatite, in stubby prisms, 0.05 mm long, clear where included in hypersthene or salite but with a slightly pseudodichroic rim elsewhere. |