Polished Topaz Imitating rough Diamonds
Two large, near-colourless rough stones weighing 50.08 and 38.18 ct were submitted to our research 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. 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.
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.