What is Garnet?
Garnet is a group of cubic nesosilicate minerals whose species and varieties differ in chemistry, colour and geological setting.
Mineralogy and structure
Reference formula: X3Y2(SiO4)3. Garnet is a mineral group, not one single species. X3Y2(SiO4)3 is the group formula: the X site is commonly occupied by calcium, magnesium, iron or manganese, while the Y site commonly contains aluminium, chromium or iron. Confirmed species should be named where composition is known. Garnet belongs to the silicates and has a cubic crystal system. Typical hardness is 6.5–7.5 on the Mohs scale and specific gravity is approximately 3.5–4.3.
Colour and appearance
Typical colours include red, orange, yellow, green, brown, black. The usual dodecahedral, trapezohedral, granular habit and vitreous, resinous lustre are useful descriptive features, but colour alone is not diagnostic.
Formation and localities
Garnet forms in or is associated with metamorphic rocks, skarns, igneous rocks, pegmatites and alluvial deposits. Important documented localities include India, Sri Lanka, Russia, Tanzania, Kenya, Madagascar, Brazil, Namibia and the United States. A precise locality and host rock are more useful than a broad colour label.
Collecting notes
Garnet should be labelled as a confirmed species, variety or group-level reference according to the evidence available for the specimen. Record colour, transparency, crystal form, matrix, locality and any treatment history.
Garnet species and varieties
This group page links to the principal species and common collector varieties: Almandine. Andradite. Grossular. Pyrope. Spessartine. Uvarovite. Demantoid. Hessonite. Hydrogrossular. Melanite. Rhodolite. Topazolite. Tsavorite.
