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Taaffeite

Rare gemstone

Field	Value
boxbgcolor	#7e5c77
boxtextcolor	#fff
name	Taaffeite
category	Oxide minerals
image	Magnesiotaaffeite-2N2S-53105.jpg
caption	Magnesiotaaffeite-2N’2S (Mg3Al8BeO16)
formula	BeMgAl4O8
IMAsymbol	Tf
strunz	4.FC.25
system	Hexagonal
class	Dihexagonal pyramidal (6mm)
Trigonal dipyramidal (m)
(magnesiotaaffeite-6N'3S and ferrotaaffeite-6N'3S)
color	Colorless, greyish violet, violet red, red, greenish, light green, pink violet, mauve
habit	Prismatic, alluvial grains
twinning	By reflection on (0001)?
cleavage	Imperfect/fair/absent
fracture	Conchoidal
mohs	8–8.5
luster	Vitreous
refractive	nω = 1.722, nε = 1.777
opticalprop	Uniaxial
birefringence	δ = 0.055
pleochroism	Weak
streak	White
gravity	3.60–3.61
diaphaneity	Transparent to translucent
references

Trigonal dipyramidal (m) (magnesiotaaffeite-6N'3S and ferrotaaffeite-6N'3S)

Taaffeite (; BeMgAl4O8) is a mineral, named after its discoverer Richard Taaffe (1898–1967) who found the first sample, a cut and polished gem, in October 1945 in a jeweler's shop in Dublin, Ireland. As such, it is the only gemstone to have been initially identified from a faceted stone. Taaffeite is a million times rarer than diamonds and comes in shades of purple, pink, red. Most pieces of the gem, prior to Taaffe, had been misidentified as spinel. For many years afterwards, it was known only in a few samples, and it is still one of the rarest gemstone minerals in the world.

Since 2002, the International Mineralogical Association-approved name for taaffeite as a mineral is magnesiotaaffeite-2N'2S.

Discovery

Taaffe bought a number of precious stones from a jeweller in October 1945. Upon noticing inconsistencies between the taaffeite and spinels, Taaffe sent some examples to B. W. Anderson of the Laboratory of the London Chamber of Commerce for identification on 1 November 1945. When Anderson replied on 5 November 1945, he told Taaffe that they were unsure of whether it was a spinel or something new; he also offered to write it up in Gemologist.

Properties

In 1951, chemical and X-ray analysis confirmed the principal constituents of taaffeite as beryllium, magnesium and aluminium, making taaffeite the first mineral to contain both beryllium and magnesium as essential components.

The confusion between spinel and taaffeite is understandable as certain structural features are identical in both. Anderson et al., classified taaffeite as an intermediate mineral between spinel and chrysoberyl. Unlike spinel, taaffeite displays the property of double refraction that allows distinction between these two minerals.

Usage

Because of its rarity, taaffeite is used only as a gemstone.

Formation and occurrence

Taaffeite occurs in carbonate rocks alongside fluorite, mica, spinel and tourmaline. This extremely rare mineral is increasingly found in alluvial deposits in Sri Lanka and southern Tanzania, as well as lower grade taaffeite in limestone sediments in China.

References

Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
Dept. Mineralogy, British Museum, June 7 1951 [http://rruff.info/uploads/MM29_765.pdf Taaffeite, a new beryllium mineral, found as a cut gem-stone.] Retrieved February 2015
Anderson, B.W., Payne, C.J., and Claringbull, G.F., (1951) [http://rruff.info/uploads/MM29_765.pdf Taaffeite, a new beryllium mineral, found as a cut gemstone]. Mineralogical Magazine 29, pp. 765–772
1-4344-5702-8
Papers and proceedings of the International Mineralogical Association. General meeting, Mineralogical Society of America, Volume 9, [https://books.google.com/books?id=ScQZAQAAIAAJ&q=Taaffeite p. 502]
1-84537-602-1
[http://www.mindat.org/min-3863.html Magnesiotaaffeite], Mindat
[http://www.galleries.com/minerals/oxides/taaffeit/taaffeit.htm Amethyst Galleries Inc.]
0-7506-6449-5.
Institut mineralogii, geokhimii, i kristallokhimii redkikh ėlementov (1966). Geochemistry and mineralogy of rare elements and genetic types of their deposits, Volume 2. Institut mineralogii, geokhimii i kristallokhimii redkikh elementov. (English Version Publisher: Israel Program for Scientific Translations). pp. 77–79.
Geological abstracts, Issues 1–7259 (1992). Elsevier/Geo Abstracts, p. 565

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gemstones magnesium-minerals aluminium-minerals beryllium-minerals hexagonal-minerals

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