Taaffeite reacts to most gemological tests like mauve-colored spinel, but can be distinguished on the basis of its birefringence. Additional stones will undoubtedly be discovered in the future (generally misidentified as spinel) as collectors search for these rarities. Taaffeite is one of the rarest of mineral species, and surely among the very rarest and most desirable of all collector gemstones.
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|Crystallography||Hexagonal; crystals microscopic, prismatic; known chiefly as rounded pebbles and cut gemstones.|
|Colors||Colorless, greenish, pinkish, lilac to purple, bluish, bluish violet, red.|
|Density||3.60-3.62; Zincian = 3.71.|
|Stone Sizes||The originally discovered taaffeite came out of a lot of mauve spinels and weighed 1.419 carats; part of this stone was analyzed, and the remainder was recut into a gem of 0.55 carat. This was presented to the discoverer, Count Edward Charles Richard Taaffe, a Bohemian—Irish gemologist living in Dublin. A second stone identified as taaffeite weighed 0.86 carats and is now in the Geological Museum, London. A third taaffeite of 0.84 carats, identified at the Gemological Institute of America laboratory in New York, resides in the S1collection along with a dark brownish-purple gem of 5.34 carats. Many other stones have been identified, perhaps as many as 50. A Sri Lankan collector owns a flawless mauve oval weighing 13.22 carats. A 10.13 carat gray-mauve oval, lightly included, resides in another private collection, as well as a pink oval of 11.24 carats and numerous smaller stones. A Burmese taaffeite of 3.04 carats, also pale mauve has been reported.|
|Luminescence||Distinct green in UV and X-rays.|
|Spectral||Not diagnostic; however, the spectra of gem taaffeites are similar to those of red and blue-violet spinels containing Fe and Cr.|
|Formula||BeMg3Al8O16 + Fe, Mn, Zn, V, Cr.|
Optics: o= 1.721-1.724; e = 1.717—1.720.
Zincian: o= 1.730; e= 1.726; birefringence = 0.004.
Inclusions: Inclusions reported in Sri Lankan taaffeites include: phlogopite; garnet; muscovite; apatite; spinel; zircon; fingerprints of negative crystals and spinels; and partly healed liquid fractures. The apatite crystals tend to be well-formed prisms, colorless to yellow. The apatites, negative crystals, and fingerprints are commonly observed.
Occurrence: In metamorphosed limestones and skarns; also as rolled pebbles, very rarely (China) in crystals (microscopic).
China: reported in dolomitized limestone in Hunan Province (o= 1.720; e=1.741; birefringence = 0.006).
Burma: (o= 1.720; e= 1.716; birefringence=0.004; S.G. = 3.59).
USSR: (o= 1.735; e= 1.726; birefringence =0.009).
Sri Lanka: assumed origin of most known cut gems.
Note: Polytype of taaffeite discovered in the Musgrave Ranges, Central Australia (o= 1.739: e= 1.735; S.G. =3.68).
Comments: Taaffeite reacts to most gemological tests like mauve-colored spinel, but can be distinguished on the basis of its birefringence. Additional stones will undoubtedly be discovered in the future (generally misidentified as spinel) as collectors search for these rarities. Taaffeite is one of the rarest of mineral species, and surely among the very rarest and most desirable of all collector gemstones.
A zincian taaffeite With ZnO as high as 4.66% has been reported. The material is reddish violet due to Mn and Cr and has higher refractive indices and S.G. than normal taaffeite. A red gemstone (1.02 carats) was reported from Sri Lanka with the following properties: R.l. = 1.717—1.721, birefringence =0.004, S.G. =3.61, hardness= 8+, hexagonal, slight reddish luminescence, Cr presents (emission line in spectrum). This was first thought to be taaffeite, later considered a new species and named taprobanite (after Taprobane, ancient name of the island of Sri Lanka). This material was eventually proven to be a taaffeite after all, and the name taprobanite has been dropped from use. However, the intense research into this problem led to a revised formula for taaffeite.
Name: After Count Taaffe, Bohemian-Irish gemologist, who discovered the first stone in 1945.