Garnet is the birthstone for January, and has been used since the Bronze Age.

The Garnet groups of minerals show crystals with a habit of rhombic dodecahedrons and trapezohedrons. They are nesosilicates with the same general formula, A3B2(SiO4)3. The chemical elements in Garnet include calcium, magnesium, aluminum, iron2+, iron3+, chromium, manganese, and titanium.

Garnets show no cleavage and a dodecahedral parting. Fracture is conchoidal to uneven; some varieties are very tough and are valuable for abrasive purposes. Hardness is 6.5 - 7.5, specific gravity is 3.1 - 4.3, luster is vitreous to resinous, and they can be transparent to opaque.

The name "Garnet" comes from the Latin granatus, a grain possibly in reference to malum garanatum (pomegranate) a plant with red seeds similar in shape, size and color to some Garnet crystals.

There is a misconception that Garnets are only a red gem but in fact they come in a variety of colors including purple, red, orange, yellow, green, brown, black, or colorless. The lack of a blue Garnet was remedied in 1990's following the discovery of color-change blue to red/pink material in Bekily, Madagascar but these stones are very rare.

In daylight, Garnet color can be shades of green, beige, brown, gray and rarely blue, to reddish or purplish/pink color in incandescent light. The color change of these new Garnets is often more intense and more dramatic than the color change of top quality Alexandrite which is frequently disappointing, but still sells for many thousands of dollars (US) per carat.

Six common varieties of Garnet are recognized based on their chemical composition. Garnet varieties are pyrope, almandine or carbuncle, spessartite, grossularite (varieties of which are hessonites or cinnamon-stone and tsavorite), uvarovite and andradite. The Garnet makes up two solid solution series; 1. Pyrope-almandine-spessarite or 2. Uvarovite-grossularite-andradite.