Учебное пособие Иркутск 2006 Рецензент (1) - Учебное пособие
Dec 07, 2016· The greater the range of sphere diameters, the more intensively white, opaque or "potchy" the stone becomes, and the less intense is any colour display. Potch from Lightning Ridge is often deeply pigmented and opaque grey to black, and is invariably the underlying base to the best gem quality black opals.