Banalsite

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Banalsite
General
Category Tectosilicate
Formula
(repeating unit)
BaNa2Al4Si4O16
Strunz classification 09.FA.60
Crystal symmetry Orthorhombic 2/m 2/m 2/m
Unit cell a = 8.496(2) Å, b = 9.983(2) Å, c = 16.755(3) Å; Z = 4
Identification
Color White
Crystal habit Rarely showing traces of crystal faces; coarsely crystalline to compact, massive
Crystal system Orthorhombic
Cleavage Good on {110} and {001}
Mohs scale hardness 6.5
Luster Vitreous, pearly on cleavage
Streak White
Diaphaneity Translucent to transparent
Specific gravity 3.065
Optical properties Biaxial (+)
Refractive index nα = 1.570 nβ = 1.571 nγ = 1.578
2V angle Measured: 41°, Calculated: 52°
References [1][2][3]

Banalsite is a rare barium, sodium aluminium silicate mineral with formula: BaNa2Al4Si4O16. Banalsite is a tectosilicate of the feldspar group.

Banalsite and its strontium analogue, stronalsite (SrNa2Al4Si4O16), constitute a complete solid solution series.[4] In addition limited solid solution with calcium exists between these and lisetite: CaNa2Al4Si4O16.[5]

It was first described in 1944 for an occurrence in the Benallt Mine, Rhiw, Llanfaelrhys, Lleyn Peninsula, Gwynedd (Caernarvonshire), Wales.[2] The name is derived from the chemical symbols of its composition. It has also been reported from Långban, Värmland, Sweden and from the Kalahari manganese field, Cape Province, South Africa.[1] It has recently been reported from the nepheline syenites of the Zhidoy massif, Eastern Sayan, Siberia, Russia; the Prairie Lake complex of alkaline rocks and carbonatites, Superior Alkaline Province, northwestern Ontario, Canada; the Pilansberg peralkaline complex, South Africa; the Sakharjok alkaline complex in the Kola Alkaline Province, Kola Peninsula of northwestern Russia {the Gremyakha–Vyrmes peralkaline complex, and the Turiy Mys complex of ultramafic–alkaline rocks and carbonatites.[5]

References[edit]