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 crystalline forms but differ in chemical composition. The different species are pyrope, almandine, spessartine, grossular (varieties of which are hessonite, cinnamonite and tsavorite), uvarovite and andradite.
Granites make up two series of solid solutions: pyrope-almandine-spesartin (pyralspite), with the composition range [Mg,Fe,Mn]3Al2(SiO4)3, and uvarovite-grossular-androdite (ugrandite), with the composition range Ca3[Cr,Al,Fe]2(SiO4)3. The word garnet comes from the 14th-century English word gernet, meaning 'dark red'. It is borrowed from the Old French grenade from the Latin granatus, from granum ('grain, seed'). This is possibly a reference to mela granatum or even to pomum granatum ('pomegranate', Punica granatum), a plant whose fruit contains abundant bright red seed coats (arils) that are similar in shape, size and colour to some garnet crystals.
Hessonite garnet is also called "gomed" in Indian literature and is one of the 9 stones in Vedic astrology that make up Navaratna.
Garnet species are found in all colours, with reddish hues being the most common. Blue garnets are the rarest and were first reported in the 1990s. The light transmission properties of garnet species can range from transparent gem-quality specimens to opaque crystals used for industrial purposes as abrasives. The mineral's luster is classified as vitreous (glass-like) or resinous (amber-like). Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this group of minerals has a Mohs scale hardness range of about 6.0 to 7.5. Harder species, such as almandine, are often used for abrasive purposes.
Red garnets were the most commonly used gemstones in the late ancient Roman world and art during the migration period of the "barbarian" peoples who took over the territory of the Western Roman Empire. They were especially used inlaid in gold cells in the cloisonné technique, a style often called simply cloisonné garnet, found from Anglo-Saxon England, as at Sutton Hoo, to the Black Sea. Thousands of Tamraparniyan shipments of gold, silver and red garnet were made in the ancient world, including to Rome, Greece, the Middle East, Serica and the Anglo-Saxons.
Recent finds such as the Staffordshire Hoard and the Winfarthing Woman skeleton pendant in Norfolk confirm the existence of a gem trade route to South India and Tamraparni (ancient Sri Lanka), known from ancient times for gemstone production. Pure garnet crystals are still used as gemstones. Gemstone types come in shades of green, red, yellow and orange. In the US, it is known as the birthstone of January.
The garnet family is one of the most complex in the jewellery world. It is not a single species but is composed of several species and varieties. Garnet is considered to be the birthstone of January. It is also the birthstone of Aquarius and Capricorn in tropical astrology.
In Persia, this birth jewel was considered a talisman from the forces of nature, such as thunder and lightning. It was widely accepted that garnet could signal approaching danger by turning pale.
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