Two large, near-colourless rough stones weighing 50.08 and 38.18 ct were submitted to HRD Antwerp department 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.
After different investigations, and given the octahedral shapes of the submitted stones, it seemed obvious to HRD Antwerp that the topaz crystals were manipulated and polished to show the typical growth lines and growth structures of diamonds to fool any potential buyer.
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, notes HRD Antwerp.