Unusual Inclusions in Natural Emerald from Chivor
Nailhead inclusions are commonly associated with hydrothermal synthetic emeralds and occasionally found in flux-grown emeralds as well (G. Choudhary and C. Golecha, “A study of nail-head spicule inclusions in natural gemstones,” Fall 2007 G&G, pp. 228–235; N. Renfro et al., “Inclusions in natural, synthetic, and treated emerald,” Winter 2016 G&G, pp. 402–403). Interestingly, similar inclusions have also been observed in natural emeralds. These inclusions occur when a tiny particle or platelet of a foreign substance becomes trapped within the host mineral during crystal growth. As the crystal continues growing, a conical void develops behind the particle, which typically captures various forms of matter, including liquids and gases (Choudhary and Golecha, 2007).
While examining a 1.40 ct rough Colombian emerald sourced from the Chivor district in Boyacá, the authors encountered growth blockage inclusions resembling nailhead inclusions. Unlike the jagged shape typical in Colombian emeralds, these three-phase inclusions exhibited a tubular form and were oriented parallel to the c-axis of the crystal. Using Raman spectroscopy, euhedral albite crystals were identified at both ends of the inclusion (see above), suggesting a strong interaction between the mineralizing fluids and the host rock, where the fluids may have dissolved albite from the rock and become enriched with its constituents. This could be due to previous alteration processes within the host rock resulting in the replacement of preexisting minerals by albite, known as albitites (A. Cheilletz and G. Giuliani, “The genesis of Colombian emeralds: A restatement,” Mineralium Deposita, Vol. 31, No. 5, 1996, pp. 359–364).
