While turquoise is well known to gemologists and highly valued as a massive lapidary material, crystalline turquoise is extremely rare and was first recognized by geologists in 1909 at the Bishop copper prospect in Lynch Station, Campbell County, Virginia. The locality was rediscovered by collectors in 1941 but has since been largely forgotten.
Recently, we studied and photographed a 31.14 ct mineral specimen from the Bishop mine displaying turquoise crystals (figure 1). These euhedral triclinic crystals were situated on the quartz matrix in the form of tight clusters and single crystals (figure 2). Laser Raman microspectrometry confirmed the crystals as turquoise, and energy-dispersive X-ray fluorescence analysis revealed the dominant presence of copper.
This was our first opportunity to examine actual turquoise crystals, a form of turquoise rarely encountered by gemologists.
John I. Koivula is analytical microscopist, and Nathan Renfro is senior manager of colored stone identification, at GIA in Carlsbad, California.
While turquoise is well known to gemologists and highly valued as a massive lapidary material, crystalline turquoise is extremely rare and was first recognized by geologists in 1909 at the Bishop copper prospect in Lynch Station, Campbell County, Virginia. The locality was rediscovered by collectors in 1941 but has since been largely forgotten.
Recently, we studied and photographed a 31.14 ct mineral specimen from the Bishop mine displaying turquoise crystals (figure 1). These euhedral triclinic crystals were situated on the quartz matrix in the form of tight clusters and single crystals (figure 2). Laser Raman microspectrometry confirmed the crystals as turquoise, and energy-dispersive X-ray fluorescence analysis revealed the dominant presence of copper.
This was our first opportunity to examine actual turquoise crystals, a form of turquoise rarely encountered by gemologists.
John I. Koivula is analytical microscopist, and Nathan Renfro is senior manager of colored stone identification, at GIA in Carlsbad, California.
