Banalsite

Banalsite
General
Category	Tectosilicate
Formula; (repeating unit)	BaNa2Al4Si4O16
Strunz classification	9.FA.60
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) ; H-M symbol: (mm2)
Space group	Iba2
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
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][4]

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.[5] In addition limited solid solution with calcium exists between these and lisetite: CaNa₂Al₄Si₄O₁₆.[6]

It was first described in 1944 for an occurrence in the Benallt Mine, Rhiw, Llanfaelrhys, Lleyn Peninsula, Gwynedd (Caernarvonshire), Wales.[3] 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.[2] 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).[6]

References

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[1] Mineralienatlas

[Handbook-2] ttp://rruff.geo.arizona.edu/doclib/hom/banalsite.pdf Handbook of Mineralogy

[Mindat-3] ttp://www.mindat.org/min-504.html Mindat.org

[Webmin-4] ttp://www.webmineral.com/data/Banalsite.shtml Webmineral data

[5] Liferovich, Ruslan P., et. al., The Crystal Structure of Stronalsite and a Redetermination of the Structure of Banalsite, The Canadian Mineralogist, Vol. 44, pp. 533-546 (2006)

[Liferovich2-6] Liferovich, Ruslan P., et. al., Paragenesis and Composition of Banalsite, Stronalsite, and Their Solid Solution in Nepheline Syenite and Ultramafic Alkaline Rocks, The Canadian Mineralogist, Vol. 44, pp. 929-942 (2006)