Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms but differ in chemical composition. The different species are Pyrope, Almandine, Umba River, Spessartine, Grossular, Uvarovite and Andradite. Garnet is 6.5 – 7.5 on the Mohs hardness scale.
Garnet is January’s birthstone, and the gem for the second wedding anniversary. It is available in a rich palette of colors: greens, oranges, yellows, pinkish oranges, deeply saturated purplish reds, and even some blues.
Red garnet is one of the most common and widespread of gems. But not all garnets are as abundant as the red ones. A green garnet, tsavorite, is rare and needs rarer rock chemistries and conditions to form.
Demantoid is a rare and famous green garnet, spessartite is an orange garnet, rhodolite is a beautiful purple-red, andradite and grossular are a yellowish green color.
All garnets have essentially the same crystal structure, but they vary in chemical composition. There are more than twenty garnet categories, called species, but only five are commercially important as gems. Those five are pyrope, almandine, spessartite, grossular, and andradite. A sixth, uvarovite, is a green garnet that usually occurs as crystals too small to cut. It’s sometimes set as clusters in jewelry. Many garnets are chemical mixtures of two or more garnet species.