Photo of Taaffeite in Processed & Rough Form
Taaffeite is a mineral with a hardness of 8 out of 10 on the Mohs scale of mineral hardness [?]. These Hexagonally structured gems are made of barium manganese aluminum oxide, their full chemical compound being BeMg3Al8O16.
Taaffeite is a very rare beryllium magnesium aluminum mineral. No other mineral has both beryllium and magnesium in its composition. It is one of the few gems to be discovered as a faceted stone instead of a rough, as most gemstones are. Rarely cut as a gem, taaffeite looks like a mauve-colored spinel, and its absorption spectrum is similar to it. But gemologists know they've found taaffeite when a stone thought to be spinel is found to be doubly refractive.
Taaffeite forms pink, mauve, or lilac, red to brown transparent to translucent hexagonal crystals. It is very hard, transparent to translucent, and has vitreous luster. It may also appear as colorless, purple, greenish, bluish-violet, bluish, and reddish. It shows dichroism, bluish in daylight and reddish in artificial light.
Taaffeite is found in Hunan Province (China), Sri Lanka, Myanmar, eastern Siberia (Russia), and South Australia.
There are taaffeite inclusions in Sri Lankan stones, in garnet, muscovite, apatite, phlogopite, zircon, spinel, healed fractures, fingerprints of negative crystals.
This rare mineral occurs in gem gravels or in skarns at the contact between sedimentary dolomite rock and and limestones with beryllium-bearing granite. It also occurs in carbonate rocks alongside fluorite, mica, spinel and tourmaline.
The gem gravels yielding taaffeite are located in Sri Lanka. A purple brown chatoyant was found there, the eye arising from parallel reflective inclusions combined with striations. Faceted crystals have also been found near Mt. Painter, Southern Australia. Lower-quality taaffeite has been found in China. Recent authorities use the name magnesio-taaffeite.
Unusually the type species is a faceted stone, originally believed to be spinel.
What distinguishes Taaffeite from Spinel?
While visually similar to spinel, taaffeite contains beryllium and shows double refraction, making it structurally unique. This optical property provides definitive separation from spinel's isometric system.
How does chemical composition affect formation?
The beryllium-magnesium-aluminum composition requires specific geological conditions, explaining its extreme rarity. Formation occurs in high-grade metamorphic environments with unusual geochemical conditions.
What explains the limited geographical distribution?
Primary deposits occur in Sri Lanka and Myanmar, with rare specimens from other locations. The specific chemical requirements for formation restrict its occurrence to regions with appropriate geological conditions.
How are optical properties related to structure?
The hexagonal crystal system produces distinctive optical characteristics including moderate birefringence. Refractive indices and pleochroism provide diagnostic criteria for identification.
What analytical methods confirm identification?
Advanced testing includes Raman spectroscopy and chemical analysis. Double refraction observation provides initial separation from similar-appearing spinel and can be observed with standard gemological equipment.
How does color zoning manifest?
Color zoning, when present, typically shows hexagonal growth patterns. Color variations range from mauve to violet, with intensity variations corresponding to trace element concentrations.
What factors determine specimen value?
Extreme rarity is the primary value factor. Color intensity, clarity, and size significantly impact value, with documented provenance adding historical importance.
The specific gravity [?] for Taaffeite is 3.61, its refractive index [?] is 1.72-1.77, and its double refraction [?] is 0.004.
History
Taaffeite is named for its discoverer, Count Charles Richard Taaffe. He first came across a faceted stone while sorting out a batch of spinel from a jeweler in 1945. For many years after, taaffeite was known only in a few samples and became famous as one of the rarest gems in the world. It was formerly called taprobanite.
The confusion between spinel and taaffeite is understandable as the two share very similar physical properties. The crucial difference is that taaffeite is doubly refractive while spinel is singly refractive.
Industrial Usages
Because of its distinction as being one of the rarest minerals, taaffeite is only used as a gemstone.
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