Rose quartz starRose quartz is the massive (ie it only rarely produces crystals with the usual hexag

Rose quartz starRose quartz is the massive (ie it only rarely produces crystals with the usual hexagonal form, see http://tinyurl.com/nfbycoc for a stunning example of the latter) pink form of quartz. It is usually translucent rather than transparent. Rose quartz forms at high temperatures in pegmatites, those last fluid and element rich crystal mushes that are the last parts of granite to crystallise and form so many of the world’s gems. It grows in the phase known as pneumatolytic, meaning it crystallises directly from the hot steam rich gaseous phase as opposed to water rich fluid phases.After much heated debate over the decades, it seems that the small fibres of a mineral similar to dumortierite are responsible for both the lovely pink colour and the occasional asterisms that some specimens display.The star need a strong point like source to display it, and it sometimes also visible in transmitted light shone directly through the stone, a rarity in asterism. They are accaused by reflection from minute needle shaped crystals that have congealed according to the hexagonal shape in which quartz crystallises with 3 axes looking down the length of the crystal intersecting at 60 degrees.Such rough is usually polished into spheres, and only occurs in few locations such as the pegmatites of the Vorondolo mountains near Antsirabe in Madagascar, that scion of what i term the gemlands (see http://tinyurl.com/k6464q6 for an explanation of this fantastic zone spread through Africa, India, Sri Lanka and Antarctica that marks the uniting of Gondwana way back in deeptime).An additional optical effect comes from the interaction of reflection and refraction (the bending of light as it enters an optical medium of different density such as from air to mineral) that makes the star appear in slightly different places for each eye, giving the illusion of the star hovering above the stone.This wonderful 12 rayed example resides in the Smithsonian gem collection.LozImage credit: Chip Clarkhttp://www.quartzpage.de/rose.htmlhttp://www.minerals.net/gemstone/rose_quartz_gemstone.aspxhttp://www.galleries.com/Rose_quartzhttp://minerals.gps.caltech.edu/ge114/lecture_topics/quartz/index.htm -- source link

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