Andradite garnet (Ca3Fe2Si3O12)
This calcium iron garnet occurs in metamorphic environments frequently as the result of alteration in bodies of impure limestone. It is generally associated with chlorite, diopside, mica and serpentine. Andradite varieties include demantoid, melanite and topazolite. Demantoid, the most sought after variety, was named for its diamond like lustre and brilliance.
From left to right- Cushion cut Demantoid Namibia, Demantoid crystal cluster Madagascar
It has a much higher dispersion than diamond and fine specimens from the Ural Mountains may exhibit a grass green hue rivalling that of emerald. Demantoid from northern Namibia is lively and full of fire but it lacks the rich vivid green of the Russian material. Radiating patterns of byssolite fibres described as “horse-tail” inclusions are a characteristic feature of this garnet. Cut stones are generally small and the limited supply of demantoid is seldom enough to meet the demand.
Grossular garnet (Ca3Al2Si3O12)
From left to right – Grossular garnet Tanga Tanzania, Grossular colour change daylight, Grossular colour change incandescent light
From left to right – Grossular garnet on matrix Canada, Grossular garnet, “Merelani mint”, “Merelani mint” crystal Tanzania
A calcium aluminium garnet, grossular occurs in metamorphic environments. Being allochromatic pure specimens of this garnet are virtually colourless.
Hessonite is a yellow-brown to orange-red variety of grossular and cut stones usually reveal a swirling syrupy interior when louped. The name grossular is derived from the Latin name for gooseberry since this stone is found in many shades of green.
There have been rare finds of material that exhibits an “alexandrite-like” red to green colour change.
Tsavorite” a highly valued emerald green variety is coloured by traces of vanadium. Originally it was named “Tsavolith” or the stone from the Tsavo because of an early find at Voi a small town near the border of the Tsavo National Park.
From left to right – Tsavorite trilliant, Kenya, Uvarovite garnet crystal S, Africa
Uvarovite a calcium chromium silicate is the only consistently green garnet. Cut stones are rare and good mineral specimens are much sought after by collectors.