| Text Description: |
Medium-gray (N5) hypersthene basalt, with seriate, intergranular texture. The most conspicuous crystals are of plagioclase, up to 3 mm in size, with a median composition ranging from An64 to An49 in different specimens. The sparse salite as much as 0.5 mm in size, has nZ 1.716 and nX 1.688. This suggests a composition of about En72Fs28. Olivine is very rare, and is characterized by a heavy reaction border and segregations of opaque material, apparently magnetite, along cleavage planes. Hornblende, which has a heavy resorption border of clinopyroxene, is very rare. Similar borders are also found on some grains of olivine and hypersthene. Magnetite and apatite are common accessories; the latter may be clear, where enclosed in hypersthene for example, or pseudodichronic, where exposed to reaction with the last part of the magma to crystallize. The groundmass consists of plagioclase laths, clinopyroxene granules, and interstitial orthoclase (?). Tridymite lines fractures and cavities, and is, in part, pseudomorphous after cristobalite. |