Unlike some other gems, garnets can possess any of a number of chemical configurations. The name "garnet" is actually a blanket term for all these crystals, which share similar physical properties.
The general chemical formula for a garnet is A3B2(SiO4)3, where A can be calcium, magnesium, iron, or manganese, and B can be aluminum, iron, chromium, or in rare instances, titanium. The most common forms are pyrope (magnesium and aluminum), almandine (iron-aluminum), and rhodolite (a pyrope-almandine combination). Other common variations include spessartine (manganese-aluminum), grossular (calcium-aluminum), andradite (calcium-iron), and uvarovite (calcium-chromium). It usually forms a dodecahedral crystal and has a mineral hardness of 6.5 to 7.5.
Garnets are most commonly a dark red hue, but because it has so many chemical variations is can be found in any color except blue. A few garnets even change color when viewed under natural or incandescent light. Because of this, garnets are sometimes mislabeled (either creatively or misleadingly) as, for example, "American ruby" or "Oregon jade".
The word "garnet" is derived from the Latin word granatus, "grain", referring to the way crystals resemble grains or seeds embedded in the crystalline matrix. It has been used as a gemstone since prehistory, but was first used industrially to coat sandpaper in 1878. Today, industrial use of garnets outpace its use as a gemstone by about five hundred times.
Ancient Egyptians were known to use garnet gemstones as early as 3500 BC. Asiatic tribes carved garnets into bullets in the belief that their fiery color would inflict more deadly wounds. In ancient Greece, Alexander the Great popularized the cutting of cameos from gemstones and garnets (mainly pyrope, from Greek pyropos meaning "fire-eyed") were widely used for this purpose. Persians considered garnet to be a royal stone suitable for bearing the image of their king.
Garnet is still known as the gem of faith, constancy, fidelity and truth. It is inexpensive and often used in children's jewelry. It is mined both for industry and jewelry throughout the world, included the United States, Africa, India, Sri Lanka, and Brazil.
Garnet is the birthstone for the month of January and is the symbolic gemstone for the second wedding anniversary.