Garnet
Not one mineral but a whole silicate group — January's birthstone, most familiar in deep red.
Also known as: Garnet group
beginner Metamorphic rocks worldwide
What it is
Garnet is a group of closely related silicate minerals sharing a common crystal structure but differing in composition, which spans a series from almandine and pyrope (the classic reds) through spessartine (orange), grossular (including green tsavorite) to andradite (including brilliant green demantoid). Hardness ranges across the group from about 6.5 to 7.5 on the Mohs scale.
Most garnet is untreated, which is unusual among coloured gems and a genuine selling point. Red garnets are abundant and inexpensive, while green demantoid and tsavorite are rare and valuable. Sources are worldwide, including Africa, India, Sri Lanka and the United States. Garnet is the traditional birthstone for January.