Banal

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Banal
General and classification
chemical formula BaNa 2 [Al 4 Si 4 O 16 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.FA.60 ( 8th edition : VIII / J.07)
76.01.06.01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-pyramidal mm 2
Space group Iba 2
Lattice parameters a  = 8.54  Å ; b  = 10.01 Å; c  = 16.79 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 6.5
Density (g / cm 3 ) measured: 3.065; calculated: 3.073
Cleavage good after {110} and {001}
colour colorless, white to creamy white, gray
Line color White
transparency translucent; transparent in thin layers
shine Glass gloss, pearlescent
Crystal optics
Refractive indices n α  = 1.570
n β  = 1.571
n γ  = 1.578
Birefringence δ = 0.008
Optical character biaxial positive
Axis angle 2V = measured: 41 °; calculated: 52 °
Other properties
Special features Luminescence

Banalsite is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the crystal system with the chemical composition BANA 2 [Al 4 Si 4 O 16 ], and thus forms the barium analogue of (later discovered) Stronalsits (SRNA 2 [Al 4 Si 4 O 16 ]).

Banalsite rarely develops clearly visible crystal faces. It is usually found in the form of coarse-grained to massive mineral aggregates of white color and line color . The rare, glass-shining crystals are translucent and only transparent in thin layers. Fresh cleavage surfaces show an iridescent mother-of-pearl sheen .

Special properties

Many banal sites show a yellow-green fluorescence under short to medium - wave UV light and a weak bluish-white (very rarely also deep red) fluorescence under short-wave UV light , which changes to green phosphorescence when the UV source is removed.

Etymology and history

The name banalsite is an acronym formed from the symbols of the chemical elements barium (Ba), sodium (Na), aluminum (Al) and silicon (Si) involved in the compound .

Banalsite was first discovered in the "Benallt Mine" near Rhiw (Llanfaelrhys) on the Welsh peninsula Lleyn and described in 1944 by W. Campbell Smith, FA Bannister and MH Hey.

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of banalsite belonged to the mineral class of "silicates and Germanates" and there to the general ward of the " framework silicates (tectosilicates)" where he eponymous member of anorthoclase anorthite Banalsit- Series with the other members albite , andesine , anorthite , anorthoclase , bytownite , dmisteinbergite , filatovite , labradorite , oligoclase , stronalsite and svyatoslavite is within the large group of feldspars .

Since 2001, fixed by the International Mineralogical Association used (IMA) 9th edition of Strunz'schen systematic mineral also assigns the banalsite in the class of "silicates and Germanates" one, but there in the new department of " framework silicates (tectosilicates) without zeolitic H 2 O “. This section is further subdivided according to the presence of further anions in the chemical formula, so that the mineral can be found in the sub-section "Tectosilicates (tectosilicates) without additional anions" according to its composition, where it only belongs to group 9 together with stronalsite .FA.60 forms.

The systematics of minerals according to Dana also assigns the banalsite to the class of "silicates and germanates" and there in the department of "framework silicates with Al-Si lattice". Here he is together with Stronalsit, Lisetit and Svyatoslavit in the "Banalsitgruppe" named after him with the system no. 76.01.06 to be found in the subsection " With Al-Si grid ".

Education and Locations

Banalsite forms in small veinlets within manganese - ores and lenses of metamorphic remodeled shales . There it occurs in paragenesis with alleghanyite , barite , calcite , jacobsite and tephroit, among others .

Banalsite has been detected at 15 sites worldwide (as of 2010): In the Sierra de las Minas in Guatemala, the "Shiromaru Mine" on Honshū (Japan), near Mikkelvik in the Norwegian municipality of Karlsøy , in the Zhidoiskii massif of the Irkutsk region and the Chibinen on the Kola Peninsula in Russia, on the manganese fields of the Kalahari and in the Pilansberg Complex near Rustenburg in South Africa, in the Swedish mining community of Långban and on Santa Rita Peak in San Benito County (California) in the USA.

Crystal structure

Banalsite crystallizes orthorhombically in the space group with the lattice parameters a  = 8.54  Å ; b  = 10.01 Å and c  = 16.79 Å and 4 formula units per unit cell .

See also

Individual evidence

  1. ^ A b Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 697 .
  2. ↑ a b c Webmineral - Banalsite (English)
  3. ↑ a b American Mineralogist Crystal Structure Database - Banalsite (English, 2006)
  4. ↑ a b c d Banalsite at mindat.org (engl.)
  5. ↑ Mindat - picture of a deep red fluorescent banalsite
  6. ↑ Database of luminescent minerals - Banalsite (English)
  7. ↑ American Mineralogist Crystal Structure Database - Banalsite (2006)

literature

Web links