The Garnet group includes several different gem species:
Pyrope Garnet
Rhodolite
Spessartite Garnet
Demantoid Garnet
Tsavorite
Pyrope Garnet is red, yellowish-red or purplish-red in colour. The red colour is created by the presence of iron within the gemstone, usually with the addition of chromium. Without their presence, pure Pyrope would be colourless. It is occasionally confused with Ruby, Red Spinel, paste or Tourmaline.
It is often free from inclusions, though occasionally these may be in the form of needles. Pyrope Garnets are normally faceted and, during the 19th Century, were made very popular with the rose cut.
The association of Pyrope with Diamond as a mineral is well known, and the finding of pebbles of this Garnet in river beds or on the surface of desert sands has in several cases led to important discoveries of Diamond pipes or deposits.
Localities include South Africa, Sri Lanka, USA and Russia.
The distinctions between Pyrope and Almandine Garnet are arbitrary. Almandines tend to be a brownish red to purplish red colour, or pale to deep mauve. No internationally accepted name exists for the intermediate range of Garnets which fall between Pyrope and Almandine; however, Garnets within this range which are a pleasant light purplish red colour are often sold under the name Rhodolite.
Spessartite Garnet occurs in a yellowish orange, red or brownish red colour, resulting from the presence of manganese. Some of these stones have a somewhat similar appearance and colour to some hues of Hessonite Garnets of the Grossular Garnet species, and thus may be mistaken for them.
Inclusions can include wavy feathers, which consist of liquid droplets and which frequently have a shredded appearance.
Spessartite Garnet occurs in granite pegmatites in Sri Lanka, Myanmar, Brazil and Madagascar. Aside from these major sources, it can also be found in California, USA, New South Wales, Australia and Namibia.
Demantoid garnet is a variety of Andradite Garnet. It is green and yellow-green in colour, but is rarely yellow. Chromium is responsible for the colour of the green stones.
Characteristic inclusions of Demantoid Garnets consist of fibrous collections of asbestos mineral, which are termed ‘horsetail’ inclusions. The presence of these inclusions is diagnostic for Demantoid, and these curving fibres are present in nearly all stones.
The Ural Mountains in Russia supply most gem-quality Demantoid, which occurs mainly as rolled pebbles and rounded crystals in alluvial deposits.
Tsavorite is Green Grossular Garnet ranging in colour from bright bluish green to yellowish green. Vanadium is thought to create the colour, though some stones also contain chromium.
Green Grossular Garnet is found in the metamorphic rocks of Kenya, Tanzania and Pakistan. In the 1960s a deposit containing particularly high quality green Garnet was found in the Tsavo area on the Kenya-Tanzania border. This has led to the name Tsavorite (or sometimes Tsavolite) being used for Grossulars of this colour from all sources.