Another interesting composite – Diamonds and Rock Crystal
Author: Gagan Choudhary
(This article was first appeared in Gems & Jewellery, Vol. 19, No. 3, pp 12 – 13)
“Innovative minds who try to develop new materials on a regular basis for deceiving and making good profits are currently active in the trade”. This was the conclusion of my article ‘A new type of composite - Beryl & Glass’ appeared in Gems & Jewellery, Spring 2010, Volume 19, No. 1. Since writing the mentioned article, we have seen many such and other composite specimens submitted for identification at the Gem Testing Laboratory of Jaipur, India. In the series, these innovative minds have produced something really unusual which I have not seen anywhere before. However, studying such samples is always a pleasure.
The submitted specimen was colourless weighing 38.94 carats and measured approximately 20.94 x 20.77 x 15.95 mm (figure 1). It was triangular in shape reminiscent of a curved ‘macle’. The sample was presumed to be a rough diamond by the depositor. However, the specimen was proved to be a composite.
Figure 1: This triangular specimen weighing 38.94 carats, reminiscent of a curved ‘macle’ was a composite consisting fine chips of rough diamonds stuck over a rock crystal. Also note the range of shapes of diamond chips.
The preliminary observations were enough to identify the specimen as composite. It consisted of fine chips or flat crystals of rough diamond stuck over a colourless material, fashioned as curved triangle (see again figure 1). This was created mainly to imitate an aggregate crystal of diamond. The specimen displayed a characteristic adamantine lustre which indicated the embedded chips as diamonds; in addition the shapes varied from triangular (macle) to pseudo-hexagons and irregular associated with diamond rough. The junctions appeared much duller and whitish, often containing some yellowish / brownish substance which gave the impression of iron staining or penetration of some epigenetic substance in surface cavities. The sample was still observed under the microscope for a thorough study.
Under magnification, individual pieces of diamond chips were very much evident displaying a range of shapes as discussed earlier with a dull whitish matrix and yellowish / brownish substance (figure 2). Many of these diamond chips also displayed characteristic triangular surface markings ‘trigons’ (figure 3). Further, some areas also displayed flattened gas bubbles and / or uneven patches of the glue (figure 4) used to fix the chips on the surface of the inner colourless substance. This central material was still unidentified.
Figure 2: Individual pieces of diamond chips are very much evident displaying a range of shapes with an adamantine lustre. Note the dull whitish matrix and yellowish to brownish substance. Magnified 45x
Figure 3: Many of these diamond chips also displayed characteristic triangular surface markings ‘trigons’. Magnified 60x
Figure 4: Some areas also displayed flattened gas bubbles and / or uneven patches of the glue used to fix the chips on the surface of the inner colourless substance. Magnified 60x
Ultraviolet light plays an important role in identification of composite gem materials as also discussed in previous articles. In this specimen as well, the reaction was not otherwise; it displayed the expected results. Since diamonds have a variable fluorescence, some of the chips fluoresced blue while some remained inert under long wave (figure 5). Further, some chips had blue fluorescence along the edges; this was the reaction of the glue used.
Figure 5: Some of the diamond chips fluoresced blue while some remained inert under long wave. Also note blue fluorescence along the edges of many chips which was due to the glue used.
Measurement of the gemmological properties proved to be useful in identifying the central part of this composite. Refractive index could not be measured because of the rough surface of the sample; although it was readily identified as diamond. Even if polished, it would not have been showing the reading because of the limit of the gemmological refractometer. Hydrostatic specific gravity was measured at 2.65; this was not the accurate value, but was sufficient enough to give good indications, as majority of the portion in the specimen was the central piece. Under polariscope, the sample displayed an anisotropic reaction and fortunately displayed a partial optic figure. The optic figure was resolvable at two points diametrically opposite to each other, where a green central spot with a pink rim was observed (figure 6). Such patterns are typically observed in ‘Bull’s eye’ optic figures of crystalline quartzes. Specific gravity value at around 2.65 and this partial bull’s eye optic figure were enough to identify the central piece as rock crystal. No inclusions were visible in this central part of the specimen; hence conclusion of natural and synthetic origin was still under the question.
Figure 6: A partial bull’s eye optic figure with green central spot and pink rim was resolved in the specimen, which identified the central piece as quartz
Conclusion of natural and synthetic origin could only be drawn on the basis of FTIR analysis. IR spectrum in the region 4000 to 3000 cm-1 (figure 7) displayed peaks at around 3860, 3775, 3645, 3560, 3480, 3380, 3300, 3200 and 3120 cm-1. The peak at 3480 cm-1 is typically associated with natural rock crystal.
Figure 7: IR spectrum in the region 4000 to 3000 cm-1 concluded the origin of the central specimen. The peak at 3480 cm-1 is associated with natural rock crystals.
On the basis of FTIR analysis, reactions under polariscope and microscopic observations, the components of this composite were identified as chips of diamonds and natural rock crystal. Although identification of this specimen as a composite was not a problem, awareness and careful observations are necessary. Such specimens again remind us of the changing concepts in gemmology, courtesy the innovative minds in the industry.
All photographs and photomicrographs by Gagan Choudhary