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 Mahenge Garnet rough from Mahenge, Tanzania weighs 10.96 cts, measures 13x11x9mm and is eye clean.