Home > Mineral Abstracts > CanMin Vol. 20, pp. 59-63 (1982)




Vol. 20, pp. 59-63 (1982)



Steacyite, a new name, a re-evaluation of the nomenclature of "ekanite"-group minerals


Guy Perrault
Ecole Polytechnique de Montréal,
C.P. 6079, Succ. A, Montréal, Québec H3C 3A7



J.T. Szymanski
CANMET, Department of Energy, Mines and Resources,
555 Booth Street, Ottawa, Ontario K1A 0G1


ABSTRACT

     Ekanite from the type locality (Sri Lanka), ThCa2Si8O20, is metamict and gives only a very poor Debye-Scherrer diagram; heated Sri Lanka ekanite is body-centred tetragonal, with a 7.46, c 14.96 Å. Natural ekanite from the Tombstone Mountains, Yukon Territory (Szymanski et al. 1982) has the same chemical composition and gives a powder pattern that matches that of heated ekanite from Sri Lanka.

     The crystal structure of ekanite characterized by Si8O20 sheets, space group I422, a 7.483 (3), c 14.893 (6) Å. Steacyite corresponds to Th(Na,Ca)2(K1 - zDz)Si8O20, z = 0.39, described by Perrault & Richard (1973) under the name "ekanite". The crystal structure of steacyite is characterized by discrete pseudocubic arrangements of Si8O20, space group P4/mcc, a 7.58 (1), c 14.77 (2) Å, Z = 2. Powder diagrams of ekanite and steacyite show significant differences. A Th-Ca-K silicate from central Asia was described by Ginzburg et al. (1965) under the name "ekanite"; it corresponds to Th(Ca,Na)2(K1 - zDz)Si8O20 with z between 0.23 and 0.40. Space group, cell dimensions and powder pattern are essentially identical to those of steacyite; this mineral should receive a name other than ekanite. These two minerals may define a continuous series.

     The name honors H.R. Steacy of the Geological Survey of Canada. Iraqite (Livingstone et al. 1976) gives a powder pattern identical to that of steacyite and is presumed isostructural. It corresponds to:
(REE,Th)Ca2(K1 - zDz)Si8O20, with z - 0.47.

Keywords:  new mineral name, steacyite, Ca-Na "ekanite", Saint-Hilaire, "kanaekanite", iraqite, series steacyite - Na,Ca "ekanite".


© 1982  The Canadian Mineralogist