Last week, a leading diamond grading and certification lab HRD Antwerp detected two large topaz stones fashioned to imitate rough diamonds in an apparent attempt to fool a trader. "Two large, near-colourless rough stones weighing 50.08 and 38.18 ct were submitted to our research department to determine their quality," HRD's statement reads. "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." Topaz, a silicate mineral of aluminum and fluorine, 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. This quality of colorless topaz is only worth around $5 per carat, but is increasingly being cut to fool rough diamond buyers.
As the lab explains, "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 Raman analysis, commonly used in chemistry to provide a structural fingerprint by which molecules can be identified, clearly indicated that the heavily included stones were topaz and not diamond."
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 any potential buyer.