Garnets

An isomorphous group of minerals with general formula 8[A3B2(SiO4)3]. Cubic system. Mainly dodecahedral or tetragonal trioctahedral crystals. Vitreous to resinous luster. No cleavage. Conchoidal to uneven fracture. Brittle to tough. Garnets are divided in 2 groups; ugrandite an isomorphous intermediate group of uvarovite-grossularite-andradite and pyralspite an isomorphous intermediate group of pyrope-almandine-spessartine. Some garnets show anomalous double refraction between crossed polarizing microscopes due to stress.