Silvialite, a new sulfate-dominant member of the scapolite group with an Al-Si composition near the I4/m–P4₂/n phase transition

Authors: Teertstra D.K.; Schindler M.; Sherriff B.L.; Hawthorne F.C.

Source: Mineralogical Magazine, Volume 63, Number 3, 1 June 1999 , pp. 321-321(1)

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Abstract:

Silvialite, ideally Ca₄Al₆Si₆O₂₄SO₄, is tetragonal, I4/m, Z = 2, with a = 12.160(3), c = 7.560(1) ?, V = 1117.9(8) ?³, c:a = 0.6217:1, omega

= 1.583,

= 1.558 (uniaxial negative), D_m = 2.75 g/cm³, D_calc = 2.769 g/cm³ and H (Mohs) = 5.5. It is transparent and slightly yellow, has a good {100} cleavage, chonchoidal fracture, white streak and a vitreous lustre. It occurs in upper-mantle garnet-granulite xenoliths hosted by olivine nephelinite, from McBride Province, North Queensland, Australia. The empirical formula, derived from electron-microprobe analysis, is (Na_1.06Ca_2.86)(Al_4.87Si_7.13)O₂₄ [(SO₄)_0.57(CO₃)_0.41]. Crystal-structure refinement shows disordered carbonate and sulfate groups along the fourfold axis. Silvialite is a primary cumulate phase precipitated from alkali basalt at 900-1000°C and 8-12 kbar under high f_SO₂ and f_O₂. The name silvialite, currently used in literature to describe the sulfate analogue of meionite, was suggested by Brauns (1914).

Language: English

Document Type: Research article

Publication date: 1999-06-01

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