This year at the Tucson gem shows, this author encountered an interesting new product of chatoyant devitrified glass (glass that has converted to a crystalline material) marketed as “Starburst Stone.” This material (see above) closely resembles the chatoyant glass known as Victoria Stone, which was developed in Japan by Dr. Satoyasu Iimori in the 1950s and produced for almost 40 years (http://victoriastone.sakura.ne.jp/JP-30-88-B.pdf).
John Bennett, in partnership with Artur Birkner (both based in Perth, Western Australia), began developing Starburst Stone in 2013, and this is the first year of commercially available production (approximately 100 kilograms). This devitrified glass is made from a chemical mixture that is cooled at a rate to facilitate nucleation and growth of dense networks of elongate lath-like crystals, and each batch of glass is colored by the addition of certain metals. Darker blues are achieved by adding cobalt, lighter blue by adding copper, and green by adding chromium to the glass mixture.
Standard gemological testing revealed properties consistent with manufactured glass. The RI was between 1.51 and 1.52 and varied slightly between the different colors tested. The average SG, measured hydrostatically, was 2.62. Raman analysis identified the devitrification product responsible for the chatoyancy as apatite, which was also responsible for the chatoyancy in the devitrified glass product known as Victoria stone.
Dark and light blue, green, and golden Starburst Stones are being manufactured, with additional colors in development. This new ornamental glass showing chatoyancy is a welcome addition to the gem trade. Those interested in the material once sold as Victoria Stone will certainly appreciate this very similar phenomenal glass product.
ABOUT THE AUTHOR
Nathan Renfro is analytical manager of the gem identification department and microscopist of the inclusion research department at GIA in Carlsbad, California.