Garnet is the modern American birthstone for January, established by the National Association of Jewelers (now Jewelers of America) in the 1912 list and continuing in unbroken use ever since. The list, agreed at the Kansas City convention of 1912, was the first formal industry standardisation of the birthstone tradition in the United States and remains the basis for the modern American and most international birthstone lists, with periodic minor updates by Jewelers of America and the American Gem Trade Association.

The garnet group

Garnet is not a single mineral but a group of related silicate species sharing a common cubic crystal structure but differing in chemistry and colour. The principal trade species are almandine (iron-aluminium, the deep red of most commercial garnet), pyrope (magnesium-aluminium, blood-red, the historical "Bohemian garnet"), spessartine (manganese-aluminium, orange to mandarin), grossular (calcium-aluminium, yielding the green tsavorite and the pink and orange hessonite), andradite (calcium-iron, yielding the green demantoid), and uvarovite (calcium-chromium, an emerald green but rarely in cuttable size). The January birthstone tradition covers the group as a whole, though red garnet (almandine and pyrope) is the form most commonly understood at retail.

Trade and care

Garnet as a category occupies the moderate to lower price tier in the coloured-stone trade for most species, with significant exceptions: tsavorite, demantoid (particularly Russian Ural-Mountains material), and the finest mandarin spessartine command prices in the upper tier of the coloured-stone market. Garnet has Mohs hardness 6.5 to 7.5 depending on species and is generally durable enough for everyday wear. It is rarely treated; the most common enhancement is mild surface waxing on lower-grade material, and disclosure is straightforward.