MELT-SOLID DIHEDRAL ANGLES OF COMMON MINERALS IN NATURAL ROCKS

Abstract

The melt–solid dihedral angle has been measured in a range of igneous rock types, ranging in composition from picrite, through basalt, phonolite, andesite and rhyolite, for the minerals quartz, leucite, plagioclase, olivine, amphibole and clinopyroxene. Populations of up to 104 true 3-D angles were measured in each sample using a universal stage mounted on an optical microscope. The median and standard deviation of the angle populations for each mineral are distinct (plagioclase ?25°, with standard deviation (SD) 11°; clinopyroxene ?38°, with SD 14°; olivine ?29°, with SD 13°; quartz ?18°, with SD 9°; leucite ?20°, with SD 11°), with no control by either melt composition or degree of approach of the grains to their equilibrium shapes.