Cat’s-Eye Hexagonite
A 0.50 ct purplish pink cabochon displaying chatoyancy (figure 1) was recently submitted to the New York laboratory as a ruby. Standard gemological testing revealed a spot refractive index of 1.63 and a hydrostatic specific gravity of 3.02, neither of which were consistent with the expected values for corundum. Raman analysis, along with the specific gravity and refractive index, confirmed the identity of this mineral as tremolite (figure 2).
Hexagonite, a variety of tremolite, ranges in color from red to pink to purple. Initially believed to be a hexagonal form of tremolite, and named accordingly, the mineral was later confirmed to be monoclinic (Summer 1985 Lab Notes, p. 110). This mineral can be found in facetable sizes in St. Lawrence County and Lewis County, both in the state of New York. Though typically under a carat and heavily included, a few large transparent stones have been unearthed.
Under magnification, the densely included stone displayed long silk and needles (figure 3). These inclusions, when oriented parallel to each other and the base of a cabochon, create the cat’s-eye phenomenon.
