Silvery Rutile “Tufts” in Quartz
Recently, author JG discovered a deposit of rock crystal quartz in El Dorado County in east-central California. To date, more than 1,000 quartz crystals have been recovered from a single pocket in this deposit. Almost 50 percent of those crystals contained interesting silvery gray tufts of the titanium dioxide mineral rutile (see above), which was identified using Raman spectroscopy. Rutile in quartz typically occurs as golden needles, but it can occasionally be found as reddish brown, green, or silvery gray needles.
While the cause of the star-like needle arrangement in these particular clusters is not known, it is possible that the gray rutile is overgrown on a core crystal of anatase, which is a polymorph of rutile and might influence the morphology of the cluster. Tufts of golden rutile with a similar morphology have been observed overgrown on blue core crystals of anatase by author NR, which may explain the morphology in this sample; however, it was not possible to confirm this. A similar occurrence of gray rutile overgrowth is known to occur in the material sold as “platinum quartz” from Currelo in Minas Gerais, Brazil, where it is overgrown on the other rutile polymorph, brookite (see E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Vol. 2, Opinio Verlag, Basel, Switzerland, 2005, p. 588).
While production volume of quartz with these silvery rutile inclusions remains uncertain, this deposit has already provided interesting and beautiful additions to the micro-world.
