Garnets are a group of silicate minerals, Garnet forms when a sedimentary rock with high aluminium content, such as shale, is metamorphosed. Garnet has a hardness of 6.5 to 7.5 on the Mohs scale. This piece of Lindi Garnet rough from Tanzania weighs 2.89 cts, measures 8x6x6mm and has a small viel on the edge.