Apophyllite: Gemstone Information
Apophyllite, a name well known to mineral collectors rather than gem-mologists on account of the beautiful green crystals from India, is not now a valid mineral species under that name. The names fluorapophyllite,hydroxyapophyllite or natroapophyllite should be used according to the composition of particular specimens. These species are members of the apophyllite group. Most apophyllite likely to reach the collector or gem-mologist will be fluorapophyllite which forms a series with hydrox-yapophyllite. Fluorapophyllite has the composition KCa4Si8O20 (F,OH)8H2O. It is a member of the tetragonal system, occurring in various habits with a perfect basal cleavage. The hardness and SG are 4.5–5 and 2.33–2.37. The RI is 1.530–1.536 for the ordinary ray and 1.532–1.538 for the extraordinary ray. The birefringence is small and may be positive or negative. Neither characteristic absorption spectrum nor luminescence has been recorded. Apophyllite occurs in basalts and granites, specimens from the Poona, Nasik and Mumbai (Bombay) areas of India easily excelling all others. Other world localities can be found in mineral textbooks but their specimens are rarely used ornamentally. Mont Saint Hilaire, Quebec,Canada, has produced variously coloured specimens.Apophyllite has a notably pearly lustre and may be colourless, pink,yellow or green, none being a strong shade.