![]() ![]() Pictured below are a selection of cabochons showing asterism (multiple chatoyant bands) and cat's eye (one chatoyant band). A multitude of oriented microscopic needles scatters ![]() ![]() The view through a transparent, bronzy colored cleavage sheet of ![]() Each one of the chatoyant bands results from the interaction of light with microscopic inclusions oriented at right angles to the band itself. "The focus of a star stone is not on or in the star, but above the surface - see article in Journal of Gemmology by Harold Killingback: 'Stereoscopic effect in asterism and chatoyancy' Jan/April 2005 Vol 29 No 5/6 (Alan Hodgkinson, personal communication, 2006 edit) and paper by Würthrich.Īsterism is not only seen with overhead point-source light such as from a flashlight or the sun itself, the phenomenon can also be seen in transmitted light, that is, by shining a light through the mineral from behind as seen with mica in the image below (often referred to as diasterism). These appear to be the cause of asterism in corundums from certain locals (Rossman personal comm, 2008). Currently under study and equally as facinating as the discovery of the rose quartz nanofiberous, is the discovery of nanovoids and nanorods in corundum. Though often attributed to reflection, chatoyancy results from the scattering of light from sets of various types of parallel oriented elongated inclusions such as: needles, tubes, platelets, lathes, lattice defects, and thin films - or any combination of these (Würthrich 1981 Schmetzer, 1994). The quartz three-fold symmetry dictates the lining up of fibers in a plane perpendicular to its vertical c-axis and relative to the three lateral axes which are at 120 degree angles to each other. Hense, despite its aggregate nature, the regional crystal symmetry environment allows the formation of a six ray star seen here. Within the massive material there are regions of single crystals which can span many centimeters (Rossman personal comm, 2008). Pink quartz is a rare single crystal variety colored by radiation induced electron hole centers involving Al - P substitutions it does not form stars. Rose quartz is a massive variety of quartz found worldwide in pegmatite and hydrothermal deposits. Interestingly, the rose color of the fibers themselves is due to a Fe-Ti IVCT. Following up on this report, the Caltech team studied samples from deposits around the world, isolating the same mineral in each and quantifying its unique nature with its role in producing both the rose coloration and the asterism. The star effect (asterism) itself has been attributed to the rutile needles as well.ġn 1987, the dumortierite-like fibers were reported by Applin and Hicks in rose quartz from the Ruby Range in Montana. The cause of color in rose quartz has been debated over the years attributing it even in current texts variously to manganese, titanium, intervalence charge transfer (IVCT) between iron and titanium and to Tyndall scattering by rutile inclusions. George Rossman and his graduate students, Chi Ma and Julia S. Features this small can only be imaged using a scanning electron microscope (SEM) and it was only relatively recently that their true significance became known, notably through the research of Dr. Previously unknown, the fibers are related to dumortierite and at 100-500 nm in diameter they are so small that it would take hundreds of them together to approach the thickness of a human hair. The cause of this phenomenon is the presence of impossibly small rose colored fibers which also give the quartz its subtle coloration. Its star is exceptionally sharp and the innerscape is flawless with nary a needle visible even under high power magnification. There is an almost ethereal quality to the rose quartz cabochon pictured at the left. Star Rose Quartz Cabochon 795 cts, Madagascar ![]()
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