Banalsite

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

Banalsite
General
Category	Tectosilicate
Formula (repeating unit)	BaNa2Al4Si4O16
IMA symbol	Bns[1]
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	[2][3][4][5]

Banalsite and its strontium analogue, stronalsite (SrNa₂Al₄Si₄O₁₆), constitute a complete solid solution series.^[6] In addition limited solid solution with calcium exists between these and lisetite: CaNa₂Al₄Si₄O₁₆.^[7]

It was first described in 1944 for an occurrence in the Benallt Mine, Rhiw, Llanfaelrhys, Lleyn Peninsula, Gwynedd (Caernarvonshire), Wales.^[4] 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.^[3] 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).^[7]

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Mineralienatlas
3. http://rruff.geo.arizona.edu/doclib/hom/banalsite.pdf Handbook of Mineralogy
4. http://www.mindat.org/min-504.html Mindat.org
5. http://www.webmineral.com/data/Banalsite.shtml Webmineral data
6. 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)
7. 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)