Phenakite as a rough diamond imitation

The GIA Lab regulary receives near-colorless, transparent crystal, pieces of rough, or fragments for identification, often because they were sold as, or are hoped to be, diamond.

Such was the case with a 67,94 cts near-colorless transparent crystal that was recently submitted to the East Coast Lab.

The rough was similar enough to a dodecahedron like diamond crystal. It showed abundant dissolution features, parallel growth striations, trigon like features, and orangy red included crystal.

However, initial physical indications, such as lack of either adamantine luster or dispersion (both of which could have been obscured by the irregular surface) and low heft, suggested that it was not a diamond rough crystal. Further testing revealed that the specimen was doubly refractive and uniaxial, with a spot RI of 1,65.

The last evidence, Raman Spettroscopy, confirmed the specimen was Phenakite crystal , Be2SiO4.

Interestingly, its etymology comes from Greek word phenakos, meaning “to deceive”...

From Gems & Gemology Fall 2007