STRUCTURE AND TWINNING IN MG-AND MN-RICH ZONED GARNET FROM THE TOCANTINS RHODOLITE GARNETS, TOCANTINS STATE, BRAZIL
Mineral crystal structure is a primary tool used in understanding the intricate history of geologic environments. Decoding the crystal structure of garnets enables the determination of thermal and chemical conditions in both igneous and metamorphic systems that created them. We present an examination of the crystal structure and garnet mineral chemistry on the internal structure of almandine-spessartine-pyrope garnets. By using X-ray diffraction and secondary electron microscopy we have determined that twinning is the dominant control in fracture and crystal shape. Twinning occurs as pseudomerohedral ferroelastic twin lamellae that have preferred orientation that of twin domain boundaries parallel to (101).