Armenite-thulite-albite veins at Remigny, Quebec; the second occurrence of armenite

Abstract

At R6migrry, Quebec, fractured, prehnitized and epidotized dioritic rocks are veined and sequentially mineralized with albite, armenite, manganiferous zoisite (thulite) and piedmontite. This occurrence is today the only accessible locality of armenite. The mineral occurs as sheaf-like aggregates of centimetre-long colorless prismatic crystals with hexagonal morphology. The crystals commonly show sector trrinning and patch-like microstructure consisting of fine lamellar and gleftr-li(e fwianing. Optical properties range from sharply uniaxial to shongly biaxial. Physical prgperties .determined are: H 7-8, density 2.737(12) g/cmr @*6 2.741 g/cm3), one good prismatic cleavage; stronely biaxial armenite: 2V\65 (t2),2Vx (calc.) 57.8, o 1.5505, B 1.5570, 1 L5590 (t0.M5); uniaxial armenite: o 1.556, e 1.550 (*0.001). All diffraction maxima are compatible with space-group P6cc or M/ngcc; cell edges were found to be: a l0.n20, c 13.886(18) A. Microprobe and chemical analyses indicate that the structural formula has (l) = Sie,Al: and f(2) : All, whereas sipificant variations of interchannel and channel constituents (Na, K, Ba, Sr, Ca, H2O, CO, occur on the B, C and possibly D sites; the average formula is (Ca ao.or) (Bao.egNao.rolfo .oa ))o.nal. The study of treated armenite suggests that the optical anomalies in the mineral reflect a short-rang+ordered modulated structure. This microstructure would result from stress arising throgh ordering of interchannel and channel constituents and, possibly, loss of volatile components. Armenite and associared minerals were deposited from lowtemperature (< 3@C) solutions probably related to the surrounding granodiorite,