Gem News International Gems & Gemology, Spring 2013, Vol. 49, No. 1

Musgravite from Myanmar

Musgravite from Myanmar
Figure 1. These two musgravites (0.11 and 0.24 ct) are reportedly from Myanmar. Photo by Brad Payne.
Two small, near-colorless stones reportedly from Myanmar (0.11 and 0.24 ct; figure 1) were recently loaned to GIA for examination by Brad Payne (The Gem Trader, Surprise, Arizona). Both samples had a refractive index of 1.718–1.723 and a specific gravity of 3.66 (calculated from optical measurements using a Sarin device, due to the small size of the samples). Both showed a very weak orange fluorescence to long-wave UV radiation and luminesced weak red to short-wave UV.

These properties are within the established ranges for musgravite and taaffeite, which have similar chemical composition and structure. Distinguishing between the two minerals requires Raman spectroscopy or X-ray diffraction. Conclusive identification of these samples as musgravite was accomplished by Raman spectroscopy (see L. Kiefert and K. Schmetzer, “Distinction of taaffeite and musgravite,” Journal of Gemmology, Vol. 26, No. 3, 1998, pp. 165–167). Even though several stones have been submitted to GIA’s laboratory over the years as musgravite, rarely have they been confirmed as such (see Summer 1997 Gem News, pp. 145–147; Spring 2001 Lab Notes, pp. 60–61).

Microscopic observation revealed a heavily roiled growth structure and small colorless needles and particulates scattered throughout. Also present were numerous black opaque hexagonal platelets, identified by Raman analysis as graphite (figure 2). Interestingly, the graphite platelets all appeared to be crystallographically aligned within the host musgravite.

Musgravite Close-Up
Figure 8. Hexagonal graphite platelets were the most conspicuous inclusion in the 0.24 ct musgravite. Photomicrograph by N. Renfro; field of view is 1.08 mm.
According to Mr. Payne’s supplier, Burmese “taaffeite” (which includes a small percentage of musgravite) comes from Chaunggyi, a few kilometers northwest of Mogok. Although production is quite limited, more musgravite may appear as miners become aware of this rare gem’s existence. Due to the overlap of physical properties between musgravite and taaffeite, stones suspected of being the rarer musgravite should be submitted to a qualified gemological laboratory for confirmation.

Nathan Renfro
GIA, Carlsbad