Whether worn on their own or paired with tsavorites or diamonds, the bright, vivid orange-yellow hues of Mandarin garnets bring radiant sunshine to any piece of jewellery.
Spessartine or “Mandarin” – a story of its own
Gem-quality spessartine garnets are relatively rare compared with other members of the garnet group. In the past, both the quantity and the quality of material from known sources were highly erratic. As a result, spessartine was viewed more as a collector’s curiosity than a gemstone suitable for the jewellery market.
That changed in 1992, when an important deposit was discovered in a remote part of northern Namibia near the Angolan border. The stones from this locality displayed an intense, luminous orange unlike anything previously seen. Originally named “Kunene spessartine” after the border river, they soon became famous in the trade as Mandarin garnets.
For several years, the Kunene mine produced a steady stream of gems, making Mandarin garnets very popular with traders and designers. Unfortunately, the sizes of the cut stones were generally very small, and faceted gemstones of more than 1 ct were relatively rare. With sizes of 2 to 3 ct and more, a regular supply could not be maintained, even at high prices. Mining ceased years ago, and today the market relies on dwindling older stocks of cut or rough stones.
From collector’s item to best-seller
Luckily, a second source of fine yellow-orange garnets was later found in Nigeria, extending the available size range and securing a more reliable supply. Since then, spessartine has evolved from a collector’s stone into a jewellery best-seller, and “Mandarin garnet” has become the accepted trade name for top-quality orange spessartine, regardless of origin.
Today most stones in the trade come from Nigeria and Tanzania, and rough material has again become extremely scarce. A beautifully cut Mandarin garnet - especially one above a carat size - is a modern classic whose sunny glow is as rare as it is captivating: let the sunshine in ...
Scientific background reading
Garnets are a group of minerals with extended isomorphic solid solution among its end-members. Although solid solution of five and more components is common, usually 80% of the crystal is built up by only two or three main constituents, and all garnets can be subdivided into the two solid solution series UGRANDITE (built up mainly by the end members uvarovite, grossularite and andradite) and PYRALSPITE (built up mainly by the end members pyrope, almandine and spessartine).
Pyralspite garnets with spessartine being the main component are called spessartine in the trade. Gem quality spessartine garnets usually are members of two mainly binary solid-solution series:
Spessartine-almandine series (pyrope and grossular < 10%)
Spessartine-pyrope series (almandine and grossular < 10-15%)
Chemical analyses of spessartine from the occurrence in Nigeria show that these garnets have very high spessartine contents of 89-95%, with varying small contents of both pyrope and almandine.
Refractive indices of measured stones vary between 1.801 and 1.803, density between 4.15 and 4.22 gcm-3.
Absorption spectra can be subdivided into category (a) with low almandine content and category (b), with high almandine content.
Type (a) spectra are dominated by spin forbidden bands of Mn2+. Extremely weak Fe2+[8] bands can also be identified.
Type (b) spectra show bands of Mn2+ and Fe2+.
Internal Features
The main inclusion pattern of the Nigerian spessartine garnets are healing-cracks representing thin liquid-filled cavities or fingerprint-type feathers. A distinct tabby extinction is visible under crossed polarizing filters. The tiny black inclusions and hollow-tubes typical for Namibian spessartines are not present.
Conclusion
Chemical analyses and absorption spectra show, that the spessartine garnets from the occurrence in Nigeria fall in between the binary series spessartine-almandine on one side and the binary series spessartine-pyrope on the other side. Variation of the almandine component between 1% and 6% is responsible for a variation of colours between yellow/golden yellow and brown-orange. Spessartine garnets of nice yellow and golden yellow to orange colours are sold as “mandarin garnets” in the trade.
Further Reading Reference List
BANK, H., BERDESINSKI, W. & OTTEMANN, J. (1970): Orangeroter Spessartin aus Brasilien.- Z.Dt.Gemmol.Ges. 19(3/4), 123-127.
BANK, H., Henn, U. & MILISENDA, C.C. (1999): Spessartine garnets from Nigeria.- Z.Dt.Gemmol.Ges. 48, 62-63.
JOBBINS, E.A., SAUL, J.M., STATHAM, P.M. & YOUNG, B.R. (1977): Studies of a gem garnet suite from the Umba River, Tanzania. - J.Gemmol. 16(3), 161-171.
LIND, Th., BANK, H. & Henn, U. (1993): Spessartine aus Namibia.- N.Jahrb.Miner.Mh. 12, 569-576.
LIND, Th., Henn, U. & BANK, H. (1994): Leuchtend orangefarbige Spessartine aus einem neuen Vorkommen in Namibia.- Z.Dt.Gemmol.Ges. 43 (1/2), 39-47.
LIND, Th. & HENN, U. (2000): A new find of spessartite garnets in Nigeria.- J.Gemmol. 27(3), 129-132.
MILISENDA, C.C., LIND, Th. & HENN, U. (2010): Spessartin: Vom Sammlerstein zum Topseller.-Z.Dt.Gemmol.Ges. 59(1-2), 3-17.
MEDENBACH, O., SCHMETZER, K. & KRUPP, H. (1978): Spessartin aus den Taita Hills, Kenia.- Der Aufschluß 29, 275-276.
SINKANKAS, J. & RIED, A.M. (1966): Colour-composition relationship in spessartine from Amelia, Virginia. - J.Gemmol. 10(4), 125-134.
TISDALL, F.S. (1962): Spessartines from Madagascar.- Gemmologist 26, 124-125.
