Taaffeite

Taaffeite has one of the most unusual discovery stories in gemology. In 1945, Count Edward Charles Richard Taaffe, an Irish-Austrian gemologist, was sorting a parcel of cut spinels he had purchased from a Dublin jeweler. One pale mauve stone looked like spinel but showed double refraction under a polariscope, which spinel (being isometric) cannot do.

Taaffe sent the stone for analysis, and it turned out to be an entirely new mineral. It was the only mineral ever discovered from a faceted gemstone in a jeweler's box rather than from a geological specimen in the field.

Taaffeite forms in metamorphic rocks, particularly in marble and skarn deposits. It requires beryllium, magnesium, and aluminum all concentrated together under metamorphic conditions. These requirements are so specific that taaffeite remains one of the rarest gems on Earth, with total known gem-quality production measured in the hundreds of stones.

Taaffeite is identified by its lavender to mauve color, double refraction (distinguishing it from spinel), hardness of 8, and SG of 3.60-3.62. Under a polariscope, it shows the double refraction that spinel lacks, which is exactly how Count Taaffe originally spotted it.

Distinguish from spinel (singly refractive, isometric), pink sapphire (higher RI), and amethyst (lower hardness, lower RI). The double-refraction test on a lavender stone with spinel-like appearance is the key diagnostic.