Lab Notes Gems & Gemology, Summer 2018, Vol. 54, No. 2

Large Faceted Afghanite

An exceptionally large and clean 1.91 ct faceted oval brilliant afghanite.
An exceptionally large and clean 1.91 ct faceted oval brilliant afghanite was recently submitted to GIA’s Carlsbad lab. Photo by Robison McMurtry.

Afghanite is a blue mineral named in 1968 after its discovery in Badakhshan Province, Afghanistan. It is often found in association with lapis lazuli and sodalite (R.V. Gaines et al., Dana’s New Mineralogy, John Wiley & Sons, New York, 1997, p. 1634). It has a chemical formula of (Na,Ca,K)8(Si,Al)12O24(SO4,Cl,CO3)3·H2O (Gaines et al., 1997). Since 2003, there have been only a few mentions in the literature of gem-quality afghanite (Winter 2003 GNI, pp. 326–327; Spring 2008 GNI, pp. 79–80; Fall 2011 GNI, p. 235; Spring 2015 GNI, p. 83), with no reports of finished faceted stones larger than 1.5 ct. Five gem-quality samples ranging in size from 2.87 to 7.25 ct have been reported; however, all five were cabochons and contained numerous inclusions of lazurite (Winter 2003 GNI, pp. 326–327).

For these reasons, the 1.91 ct transparent faceted oval brilliant afghanite recently submitted to the Carlsbad lab for an identification report was truly exceptional (see above). The only inclusions in the stone were minor fractures. To date, it is the largest facet-grade afghanite on record in the GIA gem identification department. Standard gemological testing revealed that the stone was doubly refractive and uniaxial, with a refractive index (RI) of 1.522 to 1.530 and a specific gravity (SG) of 2.52. These results are consistent with the published properties of afghanite (Gaines et al., 1997). Additionally, an early report on gem-quality afghanite notes that “an interesting feature of afghanite that should prove useful in its identification is its strong, bright orange fluorescence to long-wave UV radiation,” a property that this remarkable stone exhibited (Winter 2003 GNI, p. 326–327). Further confirmation of the stone’s identity was obtained by using Raman spectroscopy, which yielded a spectrum that matched that of known afghanite samples.

Hollie McBride is a staff gemologist at GIA in Carlsbad, California.