Polished Topaz Imitating Rough Diamonds: HRD Antwerp

Two large, near-colourless rough stones weighing 50.08 and 38.18 ct were submitted recently to research department of HRD Antwerp to determine their quality. The results indicated that the gemstones, believed to be diamonds, were actually topaz. Topaz is one of the colourless diamond simulants that can be found on the market, and can be easily misidentified.

This material, which is a silicate mineral of aluminum and fluorine with the chemical formula Al2SiO4(F,OH)2, has a similar density to diamond; therefore, the stones could not be identified as diamond imitations through hydrostatic measurement or the use of a 3D-scanner (volume calculation and weight) at the trader’s office.

Although this material and diamonds share a similar density, their crystals display very different growth lines and growth structures due to their particular crystallization. Topaz crystallizes in the orthorhombic system, while diamonds do so in the regular system. This means that the rough shapes of both materials look completely different from one another. Our microscopic investigation revealed internal growth planes reflecting orthorhombic growth in the two submitted gemstones.

The value of this quality of colourless topaz is believed to be not more than 5 USD/ct. worldwide, more and more topaz are cut to fool rough diamond buyers.

 

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