These gems made the Forbes list of the12 rarest and most expensive gemstonesin the world. They are as unique as meteorites from Mars, but unlike rocks from space, they can be also indisputably beautiful and brilliant.
We were fortunate to be able to collect such an impressive collection of the stones for this article. In terms of color, they generally range from near colorless to pink, or purple although we did come across a red stone once. Ironically, Spinel is known as the great imposter in gemstone history and many of the most famous Rubies in crown jewels around the world are actually Spinel.
But here, we have two extraordinarygemstonesthat themselves have often been misidentified as Spinel.
Taafeitewas first discovered in 1945 by Count Taaffe, a Dublin gemologist who found a pale mauve stone in a jeweler’s junk box. The stone resembled Spinel in appearance and properties, but ɾєⱱєɑłєԀ distinctive double refraction so it could not be Spinel. The stone was sent to the British museum for testing where they determined it to be an unknown mineral. Although its refractive index is nearly the same as Spinel, it can be differentiated by its double refraction and uniaxial negative character. Named after its discoverer, Taaffeite is the only gemstone to have been initially identified from a faceted stone. Despite a diligent search, it was not until 1949 that another stone was found in a parcel of stones from Sri Lanka. A third stone was found in 1957 by Robert Crowningshield of GIA and a fourth stone some 10 years later. Since then, more gemologists have become aware of Taafeites and stones continue to be discovered.
(2) The collector’s dream – a very light violet Taaffeite heart weighing 2.19 cts from Tunduru.
(3) This near red Taaffeite oval weighing 0.82 cts. was found by miners looking for spinels in the Ratanapura area of Sri Lanka. An extremely rare color for taaffeite and the first near red one we ever came across in more than 30 years. Distinctive crystalline inclusions of some other mineral add further mystery to this very rare and unusual gemstone.
When we initially tested the mine run stones from Tunduru in Southern Tanzania, we discovered that some of the stones that looked like Spinel could not be Spinel as they were doubly refractive. After additional testing it was determined that some of them were Taaffeites and an even smaller percentage were Musgravites.
Musgravite is a close relative of Taaffeite and it is not only one of the rarest gemstone varieties in the world, but also an attractive and scintillating gemstone in its own right.
(4)Musgravite is not only one of the rarest gemstone varieties in the world but like this 1.41 carat oval also sometimes very bright, beautiful, and exceptionally clean.
(5)A rarity among the rare, an eye clean purple Musgravite pear weighing 3.69 cts from Tunduru.
This very rare member of the Taaffeite family was discovered in 1967 and named after the name-place discovery in the Musgrave Range of South Australia. Facet quality Musgravite was not ɾєρօɾτed until 1993 and as of 2005, there were only eight Musgravite specimens, three of which were identified by Murray Burford, a Canadian gemologist. Since then a few more stones were ɾєρօɾτed, some from Sri Lanka, and some from Tanzania but in total, probably not more than 20 or 30 stones have been found to date. The largest known Musgravite weighed 5.74 carats and was sold byMulticolour.com.
From our experience and from going thɾօυɢҺ thousands of Tunduru mine run Spinels, perhaps one in five thousand can belong to the Taaffeite family. And, from those few stones that require more extensive testing, perhaps only one in ten turns out to be a Musgravite. Because of the close structural and chemical similarities between Musgravite and Taaffeite a new systematic nomenclature was proposed and accepted by the IMA (International Mineral Association). The new scientific name for Musgravite is Magnesiotaaffeite -6N3S and Taaffeite is known as Magnesiotaaffeite-2N2S, where N and S represent nolanite and Spinel nodules. Still, Musgravite and Taaffeite are the τɾɑԀє names and nobody except a few hard core mineralogists use the scientific names.
The colors of Taaffeite, Musgravite, and Spinel can be similar and there’s no way to distinguish them without gemological testing. Chemically, they are clearly related with magnesium (Mg) and aluminium (Al) as their primary constituents. However, in terms of crystallography, Spinel is cubic while Taaffeite and Musgravite are hexagonal. Overlap in Taaffeite and Musgravite properties make these species impossible to distinguish with standard gemological tests and the most convenient way to differentiate them is with Raman spectroscopy or X-ray diffraction techniques.
Cover photo courtesy ofMulticolour.com: All from the same deposit in Tunduru, Southern Tanzania: four Taffeites, one Spinel, and one Musgravite. Can you tell which one is which?
