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 minerals, feldspar group
Formula	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]