Years ago I visited the Ametrine mine offices in Santa Cruz City, and these formations were carefully pulled from the wash tables and prized as specimens - workers called them 'candles'. Interesting naturally etched form, transparent with alternating zones of purple and yellow. Formation temperature was exactly at the point between that required to distinguish between the two Quartz colors, and this is from the only natural source that I know of: Anahí Mine, La Gaiba District, Sandoval Province, Santa Cruz Department.