Home > Mineral Abstracts > CanMin Vol. 38, pp. 627-640 (2000)




Vol. 38, pp. 627-640 (2000)



Niobokupletskite, a new astrophyllite-group mineral from Mont Saint-Hilaire, Quebec, Canada


Paula C. Piilonen and Andrew M. McDonald
Department of Earth Sciences, Laurentian Univesity,
Ramsay Lake Road, Sudbury, Ontario P3E 2C6



André E. Lalonde
Ottawa - Carleton Geoscience Centre, Department of Earth Sciences,
University of Ottawa, 140 Louis Pasteur Street,
Ottawa, Ontario K1N 6N5



Robert A. Gault
Research Division, Canadian Museum of Nature,
P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada


ABSTRACT

     Niobokupletskite, ideally K2Na(Mn,Zn,Fe)7(Nb,Zr,Ti)2Si8O26(OH)4(O,F), is a new astrophyllite-group mineral found in nepheline syenite pegmatites as a late-stage mineral at Mont Saint-Hilaire. It is triclinic, P1, a= 5.4303, b= 11.924, c= 11.747, a= 112.927°, b= 94.750°, g= 103.175°.

     Niobokupletskite is transparent with a vitreous lustre. It is brittle with a perfect {001} cleavage and has an uneven to splintery fracture. It does not fluoresce under either short- or long-wave UV light. The Moh's hardness is 3-4, and the calculated density is 3.46 g/cm3. Niobokupletskite is biaxial positive with a= 1.718, b= 1.733, gcalc= 1.755; 2Vmeas= 87°. The optical orientation is Z = c with X and Y in the [001] plane. It is pleochroic with X = Y, light orange-yellow, and Z, red brown. Three distinct types of niobokupletskite have been found.

     Type 1: occurs as anhedral to subhedral, platy to tabular, light beige to yellow epitaxic growths on primary, dark brown kupletskite associated with aegirine, albite, microcline, and pyrochlore. The primary kupletskite is zoned a relatively Ti-rich core and a Nb-enriched rim.

     Type 2: occurs as a dense, fibrous, light yellow-brown overgrowth on coarse grained primary kupletskite associated with primary and secondary aegirine, albnite, calcio-ancylite-(Ce), catapleiite, microcline, natrolite, pyrochlore, and rhodochrosite.

     Type 3: occurs as overgrowths on primary kupletskite as very-fined grained bronze to silvery brown acicular crystals in sheaf-like aggregates, originally described as "witch's broom astrophyllite" by Wight and Chao in 1986 in Rocks and Minerals, 61, 182-197. It is associated with primary and seconday aegirine, albite, analcime, calcio-ancylite-(Ce), calcite, catapleiite, epididymite, fluorite, genthelvite, microcline, natrolite, pyrochlore, rhodochrosite, and wurtzite.


© 2000  The Canadian Mineralogist