The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus ("grain"), possibly a reference to the Punica granatum ("pomegranate"), a plant with red seeds similar in shape, size, and color to some garnet crystals.

Six common species of garnet are recognized based on their chemical composition. They are pyrope, almandine, spessartite, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series: 1. pyrope-almandine-spessarite and 2. uvarovite-grossular-andradite.

Properties

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).

Crystal structure

Hardness

Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this mineral group shows a range of hardness on the Mohs Scale of about 6.5 to 7.5. The harder species, like almandine, are often used for abrasive purposes.

Pyralspite garnets - Aluminium in Y site

• Almandine: Fe₃Al₂(SiO₄)₃
• Pyrope: Mg₃Al₂(SiO₄)₃
• Spessartine: Mn₃Al₂(SiO₄)₃

Almandine

Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle (though originally almost any red gemstone was known by this name). The term "carbuncle" is derived from the Latin meaning "live coal" or burning charcoal. The name Almandine is a corruption of Alabanda, a region in Asia Minor where these stones were cut in ancient times. Chemically, almandine is an iron-aluminium garnet with the formula Fe₃Al₂(SiO₄)₃; the deep red transparent stones are often called precious garnet and are used as gemstones (being the most common of the gem garnets). Almandine occurs in metamorphic rocks like mica schists, associated with minerals such as staurolite, kyanite, andalusite, and others. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle.