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 Rare & Unusual Garnet rough weighs 16.74 cts and measures 14X10X9 mm and is eye clean.