Crystallography of some lunar plagioclases

Abstract

Crystals of calcic bytownite from type B rocks have space group I1 with c approximately 14 angstroms. Bytownite crystals from type A rocks are more sodic and have space group C1, c approximately 7 angstroms. Cell parameters of eight bulk feldspar separates from crystalline rocks indicate that the range of angle gamma is about 23 times the standard error of measurement, and its value might be useful for estimation of composition. Cell parameters of seven ilmenites are close to those of pure FeTiO(3).