Micro-World Gems & Gemology, Winter 2017, Vol. 53, No. 4

Wollastonite Blizzard Within Glass

Faceted manufactured glass beads.
Figure 1. Faceted manufactured glass beads measuring approximately 8 mm in diameter. Photo by Robison McMurtry.

A collection of lovely faceted blue beads was presented to author EAS during an annual meeting of inclusion specialists at the 2017 Tucson shows. While most specimens of interest highlighted in these meetings are of extraordinary naturally occurring minerals and gem materials—some of which have appeared in this column—these rather ordinary beads were intriguing for the veritable blizzard of translucent colorless needles and short euhedral crystals that filled each one. They created a beautiful optical effect, especially when illuminated from below (figure 1). Upon acquisition, the original owner had been told these were Russian synthetic quartz, and indeed their age and azure color suggested such an origin. It came as a surprise when standard gemological testing (refractive index of 1.518, specific gravity of 2.47, and the absence of birefringence) identified the beads as glass, making the internal scene even more intriguing for its natural appearance. Raman spectroscopy at GIA’s Carlsbad laboratory identified the beads as manufactured glass, and the majority of the needles as the calcium silicate mineral wollastonite (figure 2). Additionally, relatively small blocky crystals scattered among the needles were conclusively identified as diopside (see Summer 2010 Lab Notes, p. 144).

Faceted manufactured glass beads.
Figure 2. Transmitted light reveals a blizzard of transparent wollastonite needles within the glass host, an indication of devitrification. Interspersed among the needles are blocky crystals of diopside. Photomicrograph by Nathan Renfro; field of view 2.03 mm.

Inclusions in glass such as wollastonite and diopside are indicators of devitrification, a process by which various components of the glass’s composition crystallize out when subjected to high temperatures and/or changes in temperature. The process varies according to the type of glass. This may also happen in natural glasses, as with obsidian, resulting in the attractive lapidary material known as snowflake obsidian, which sports white blooms of cristobalite crystals on a black background. Devitrified glass is also sometimes used to imitate natural gems, as seen in manufactured “meta-jade.” The beautiful blue inner world of these beads makes them a welcome addition to one’s library of inclusions.

Elise A. Skalwold, an accredited senior gemologist of the Accredited Gemologists Association, is involved in curating and research at Cornell University in Ithaca, New York. Nathan Renfro is manager of colored stones identification at GIA in Carlsbad, California.