Shungite for jewellery use.
Recently a client submitted some pieces of a black gem material they called shungite. Initially we thought they were jet, but the gemmological properties were different. According to the literature, shungite is a mineraloid consisting of more than 98% carbon (Mastarlez et al., 2000). A mineraloid is a mineral-like substance that does not have a crystalline structure and possesses chemical compositions that vary beyond the generally accepted ranges for specific minerals. Shungite was first described from a deposit near Shunga village, in Karelia, Russia, and it has been reported to contain fullerenes (molecules of carbon in the form of hollow spheres, tubes and other shapes; Reznikov and Polekhovskii, 2000).
The samples submitted by the client consisted of assorted broken fragments and some flat-backed pieces that were cut into various shapes for mounting in jewellery; we tested a 4.32 ct sample (Figure 35). It was opaque black with a vitreous lustre and a surface that showed conchoidal fracture patterns. It was inert to UV radiation and gave a black streak. The sample showed a spot RI value of 1.62 and a hydrostatic SG of 1.86. FTIR spectroscopy recorded an absorption band at ~1578 [cm.sup.-1]. According to information given in Reznikov and Polekhovskii (2000), shungite has an RI of 1.6, SG values between 1.83 and 1.96, and IR absorption between 1580 and 1575 [cm.sup.-1]. The properties we determined for the 4.32 ct sample fell within the range for shungite and not jet (which has SG = 1.20-1.30).
The client explained that shungite is commonly used by crystal healers, and is also being mounted into some unusual designer jewellery (e.g. Figure 36).
Jayshree Panjikar (firstname.lastname@example.org)
Pangem Testing Laboratory & Pangemtech
Mastarlez M., Glikson M., Stankiewicz B.A., Volkova I.B. and Bustin R.M., 2000. Organic and mineral matter in a Precambrian shungite from Karelia, Russia. In M. Glikson and M. Mastarlez, Eds., Organic Matter and Mineralisation: Thermal Alteration, Hydrocarbon Generation, and Role in Metallogenesis, Springer Science+Business Media, Dordrecht, The Netherlands, 102-116, http:// dx.doi.org/10.1007/978-94-015-9474-5_6.
Reznikov V.A. and Polekhovskii Yu.S., 2000. Amorphous shungite carbon: A natural medium for the formation of fullerenes. Technical Physics Letters, 26(8), 689-693, http://dx.doi. org/10.1134/1.1307814.
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|Title Annotation:||ORGANIC MATERIALS|
|Publication:||The Journal of Gemmology|
|Date:||Dec 1, 2015|
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