The gemstone Garnet is the official birthstone for January as adopted by the American National Association of Jewelers in 1912. It is also the stone for the Zodiac sign Aquarius.

Garnet derived its name from the Latin word granatus, meaning like a grain, which refers to the mode of occurrence wherein crystals resemble grains or seeds embedded in the matrix. They crystallize in the cubic system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show cleavage, so when they fracture under stress, sharp irregular pieces are formed They all have the same general chemical formula, A3B2(SIO4)3, where A can be calcium, magnesium, ferrous iron, or manganese, and B can be aluminum, ferric iron, or chromium, or in rare instances, titanium.

The formulas and names of common garnet species are:

Garnets species are found in many colors including red, orange, yellow, green, blue, purple, brown, black, pink and colorless. The rarest of these is the blue garnet, discovered in the late 1990s in Bekily, Madagascar. It is also found in parts of the United States, Russia and Turkey. It changes color from blue-green in the daylight to purple in incandescent light, as a result of the relatively high amounts of vanadium (about 1 wt.% V2O3). Other varieties of color-changing garnets exist. In daylight, their color ranges from shades of green, beige, brown, gray, and blue, but in incandescent light, they appear a reddish or purplish/pink color. Because of their color changing quality, this kind of garnet is often mistaken for Alexandrite.

Garnet species’s light transmission properties can range from the gemstone-quality transparent specimens to the opaque varieties used for industrial purposes as abrasives. The mineral’s luster is categorized as vitreous (glass-like) or resinous (amber-like). Hardness of garnet on the Mohs Scale is between 6.5 to 7.5. The harder species, like almandine, are often used for abrasive purposes.

Red garnets were the most commonly used gemstones in the Late Antique Roman world and they were especially used inlaid in gold cells in the cloisonné technique, a style often just called garnet cloisonné, found from Anglo-Saxon England.

Garnet's powers are said to include healing, strength, and protection and it is often worn to relieve inflammations of the skin. It is also believed to regulate the heart and blood flow and aid in curing depression. In earlier times, garnets were exchanged as gifts between friends to demonstrate their affection for each other and to insure that they meet again.