HRD Antwerp Detects Polished Topaz Presented as Rough Diamond for Grading

(IDEX Online) – Two large, near-colorless rough stones weighing 50.08 and 38.18 carats were submitted to the HRD's research department to determine their quality, HRD Antwerp reported.

The results indicated that the gemstones, believed to be diamonds, were actually topaz. Topaz is one of the colorless diamond simulants that can be found on the market, and can be easily misidentified, the HRD said on its site.

"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.

"A detailed study of the rather large inclusions also showed the presence of typical bi-phase inclusions of topaz that are as a rule not found in diamonds. After these different investigations, and given the octahedral shapes of the submitted stones, it seems obvious that the topaz crystals were manipulated and polished to show the typical growth lines and growth structures of diamonds to fool a potential buyer. The value of this quality of colorless topaz is believed to be not more than $5 per carat worldwide, and more and more topaz is cut to fool rough diamond buyers," the HRD report added.