Scapolite: Gemstone Information
For convenience, the gem-quality varieties of the tetragonal isomorphous series marialite-meionite are conflated here. Marialite is 3NaAlSi3O8NaCl and meionite 3CaAl2Si2O8CaCO3. Crystals are prismatic, usually with flat pyramidal terminations; masses are also known. The hardness is 6 and the SG 2.50–2.78 varying with composition. The total RI range for the ordinary and extraordinary rays is 1.546–1.600; crystals are uniaxial negative. Quartz varieties with overlapping values and resembling scapolite in colour are optically positive. Pleochroism for pink and violet crystals is dark blue or lavender to colourless or violet. Pale yellow stones show colourless to pale yellow. Some pink and violet specimens show absorption bands at 663 and 652 nm, from Cr and the yellow is often strongly absorbed.
Scapolite varieties may exhibit fluorescence, yellow specimens from Myanmar giving yellow to orange and some East African yellow stones a very bright yellow-green under LWUV. There are variable responses to SWUV and to X-rays with some phosphorescence reported. Marialite meionite specimens occur in regionally metamorphosed rocks, particularly in marbles. The Myanmar stone tract at Mogok has produced fine pink chatoyant specimens some of which may incline to violet; fine golden yellow to orange stones have come from Mpwapwa, Morogoro region, Dodoma, Tanzania. Massive yellow scapolite from Quebec is particularly attractive and may show a bright yellow fluorescence.The most topical account of the scapolite group minerals can be found in the recently published (2004) vol. 4B of Deer, Howie and Zussman,Rock-Forming Minerals, published by the Geological Society of London;ISBN 1862391440.Scheelite.