Spessartine Garnet: Gemstone Information

Spessartine Garnet is known from mainly granite pegmatites and aplites but also rhyolites. In granite pegmatites, the garnets are solid solutions between spessartine and almandine, with spessartine as the dominant component: they also generally contain a few percent of the pyrope component. Formed in some skarns and metasomatic manganese-rich rocks adjacent to igneous intrusions or in regionally metasomatized areas sometimes embedded in mica and mica slate. Also found in sedimentary deposits.
So far Spessartine garnet had been found only in Sri Lanka, Myanmar, Madagascar, Brazil and Australia as well as in Kenya, Nigeria and Tanzania, and in Kunene River, Namibia (mandarin garnet). It is mined in central India, Madagascar and a number of localities in the USA, including Silver Cliff, Colorado; in rhyolite from Garnet Hill, Nevada; Ramona, California; Amelia, Virginia (in 1991, a single piece, dubbed the Rutherford Lady, was found, which weighed more than 2800 carats). Other occurrences include: the LeChang Mine, GuangDong Province, China; various localities in the North-west Frontier Province, Pakistan, such as the Shigar Valley, Skardu; Nepal and Nuristan, Afghanistan.
Within the pyralspite series, spessartine forms a continuum with almandine; however, substitution by pyrope is usually less extensive largely due to incongruent geochemistry. Commonly, spessartine can also contain appreciable amounts of grossular and more rarely andradite molecules. Consequently the physical and chemical properties and appearance can vary appreciably. An example of this is an intermediate (Sp49Gr41Al5Py5)

yellowish orange ‘Mandarin’ garnet from Madagascar, with properties that do not sit well with either spessartine or grossular but fall within the ranges for pyrope-spessartine and pyrope-almandine. Orange malaya garnets from Bekily, Madagascar, with Sp59 can have up to Py24, whereas in pink stones this ratio is reversed.
Refractive Index
Largely within the range 1.79–1.81 but rare intermediates may show values out of this, e.g. yellowish orange (Sp49Gr41Al5Py5) from Madagascar with RI 1.77.
Some locality values are: Nigeria RI 1.801–1.803; Virginia 1.802; Taita Hills, Kenya 1.795–1.809; Minas Gerais, Brazil 1.803–1.805; Ramona, California 1.81; Kunene, Namibia 1.801–1.803; Madagascar 1.800–1.808.
4.179 (calculated)
Some locality values are: Nigeria 4.15–4.22; Minas Gerais, Brazil 4.15; Ramona, California 4.17; Kunene, Namibia 4.15–4.22.
Due to its idiochromatic manganese content, spessartine is always some shade of orange. This colour is frequently tempered by isomorphous replacement, particularly by the almandine molecule, which increases the brown and red component.
Spessartine can therefore be found in a range of colours: red, reddish orange, orange, yellowish brown, reddish brown, yellow and pink. Nigerian stones tend to be darker being variously described as a very deep pure red of dark tone and strong saturation, rich, deep golden orange with a touch of fiery red, intense reddish orange and deep reddish orange or burnt orange.