Garnet Garnet is a mineral that is not only valued as a beautiful gemstone but also has a powerful industrial side. Garnet is a collective name for a group of isomorphic minerals having a composition of 3R++O, R2 +++O3, 3SiO2 where R represents bivalent metals like magnesium, calcium, manganese, iron and trivalent metals like aluminium, iron, manganese and chromium. Many garnets are an admixture of the various varieties. The hardness varies from 6.5 to 7.5 on Moh's scale and specific gravity from 3.4 to 4.3. Varieties Colour is a physical property which can broadly distinguish varieties of garnets as follows: Pyrope: Mg-Al garnet, deep red in colour Almandite: Fe-A1 garnet, deep red to brownish red in colour Andradite: Ca-Fe garnet, brownish red, yellow green or black in colour Grossularite: Ca-Fe garnet. Pale green, yellow or red in colour. Spessaritite: Mn-Al garnet, deep hyacinth or brownish red in colour Uvarovite: Ca-Cr garnet, emerald green in colour. Uses Almandite and andradite are the most common varieties. Clear flawless and richly coloured garnet are used as semi-precious stones. The most important industrial use of fresh, hard garnet is as abrasive in the form of coated paper, cloth, discs and loose grains for surfacing and polishing of soft building stones. On crushing, it breaks into angular fragments which have high capillary attraction resulting in firm adhesion to cloth, paper or wheels coated with glue. Sources National Mineral Inventory - An Overview Ministry of Mines