Gis forGarnet

Garnet is a group of related stones, the most popular of which is a deep red. Until the chemical composition was known, red semiprecious gemstones were called carbuncles. Garnets have a particular chemical formula of two metals, usually calcium, magnesium or iron and aluminium, iron or chromium bound to silicon oxide - the general forumula is X3Y2(SiO4)3.