Anorthosite metamorphosed in the granulite facies, Ceilidh Hill, central Australia. Associated gabbro contains orthopyroxene and clinopyroxene. The texture is granoblastic. The bytownite plagioclase grains exhibit polysynthetic twins that terminate within the grains defining them as secondary twins. Some grains show significant lattice rotation across sharp deformation bands. (Sample CH 1) (3.2 mm)