Garnets are a group of silicate minerals, Garnet forms when a sedimentary rock with high aluminum 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 5.42 cts and measures 10x8x5 mm. Now available at New Era Gems.