Three Faceted Collector Specimens
Three stones recently submitted to GIA (see above) were found to be rare mineral species that had not previously been examined at the Carlsbad laboratory. Standard gemological testing and Raman analysis identified these specimens as wagnerite, thaumasite, and strontianite.
A 0.60 ct transparent golden yellow pear brilliant cut with vitreous luster was identified as the phosphate monoclinic crystal wagnerite, (Mg,Fe2+)2(PO4)F. Though uncommon, wagnerite occurs in various geologic settings, such as granitic pegmatites, gneisses, eclogites, and hydrothermal environments (P. Korbel and M. Novak, The Complete Mineral Encyclopedia, Gramercy, Lisse, the Netherlands, 2003). It had a specific gravity (SG) of 3.15, a refractive index (RI) of 1.568–1.580, and a biaxial positive optic nature. Wagnerite is a relatively soft and brittle mineral with a Mohs hardness of 5.0–5.5. The stone was inert under both long-wave and short-wave UV radiation. Multiphase fluid inclusions, fingerprints, graining, and color zoning features were observed with magnification.
The largest stone, a 1.72 ct transparent colorless octagonal step cut, had a relatively low SG of 1.90, an RI of 1.470–1.515, and a biaxial negative optic nature. It was inert to long-wave and short-wave UV. These properties, along with Raman testing, led to its identification as thaumasite, a silicate mineral with the chemical formula Ca3(SO4)[Si(OH)6](CO3)·12H2O belonging to the hexagonal crystal system. Magnification revealed strong doubling, spectacular radiating fibrous inclusions, reflective films, tiny crystal inclusions, and strong hexagonal angular graining. Thaumasite has a vitreous luster and a brittle nature due to its low hardness of 3.5 on the Mohs scale. Thaumasite occurs in geothermal waters or seawaters reacting with basalt and tuffs, or in areas of contact metamorphism (J.W. Anthony et al., Handbook of Mineralogy: Volume II: Silica, Silicates: Part 2, Mineral Data Publishing, Tucson, Arizona, 1995, p. 790).
The last stone we observed was a transparent pale yellow octagonal step cut with vitreous luster. It proved to be strontianite, SrCO3, an orthorhombic carbonate mineral member of the aragonite group with a Mohs hardness of 3.5. The 1.41 ct specimen was highly birefringent, with an RI of 1.511–1.661, an SG of 3.76, and a biaxial negative optic nature. It fluoresced red under long-wave UV but displayed a weak whitish reaction under short-wave UV. The stone exhibited strong doubling and fluid inclusions under magnification. Raman spectroscopy confirmed its identity. Strontianite occurs together with calcite and zeolites in hydrothermal, low-temperature veins and in cavities of volcanic rocks (Korbel and Novak, 2003).
Wagnerite, thaumasite, and strontianite are rarely seen as faceted gems due to their softness and brittleness. These collector specimens were the first of their kind to be submitted to GIA’s Carlsbad laboratory for testing. Although challenging to identify without advanced testing techniques, they bring excitement to gemologists searching for unusual faceted gems.
