Ulexite

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Ulexite
Ulexite-237263.jpg
Fibrous, lumpy ulexite from the borax open pit mine, Kramer borate deposit, Kern County , California, USA (size: 85 mm × 65 mm × 65 mm)
General and classification
other names
  • TV stone
  • Television or TV stone
chemical formula CaNa [B 5 O 6 (OH) 6 ] • 5H 2 O
Mineral class
(and possibly department) 		Borates
System no. to Strunz
and to Dana 		6.EA.25 ( 8th edition : V / H.14)
05/26/11/01
Similar minerals Howlite , magnesite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 8.82  Å ; b  = 12.87 Å; c  = 6.68 Å,
α  = 90.4 °; β  = 109.0 °; γ  = 105.0 °
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) 2.0
Cleavage perfect after {010} and {100}, good after {1 1 0}, indistinct after {110}
Break ; Tenacity uneven across the grain; brittle
colour colorless, white, gray
Line color White
transparency transparent to opaque
shine Glass gloss, silk gloss
Crystal optics
Refractive indices n α  = 1.491 to 1.496
n β  = 1.504 to 1.506
n γ  = 1.519 to 1.520
Birefringence δ = 0.028
Optical character biaxial positive
Axis angle 2V = 73 ° to 78 ° (measured), 68 ° (calculated)
Other properties
Chemical behavior slightly soluble in water

Ulexite , also known as television stone or Television stone or TV-Stein , a rarely occurring is known mineral in the mineral class of " borates " (formerly carbonates, nitrates and borates ) having the formula CaNa [B 5 O 6 (OH) 6 ] · 5 H 2 O and is therefore, chemically speaking, a water-containing calcium - sodium borate.

Ulexit crystallizes in the triclinic crystal system , but rarely developed that are visible, acicular to prismatic single crystals . It is mostly found in the form of fibrous mineral aggregates , cotton-like bulbs or compact, parallel- fiber , grape-like masses and vein fillings . Depending on the form, ulexite is colorless and transparent (single crystal) to opaque white (compact bodies). It can also take on a gray color when it is contaminated with clay minerals . In fibrous formation, the mineral shows a silk-like sheen on the surfaces.

Etymology and history

Ulexit was first described by the Hamburg chemist Georg Ludwig Ulex around 1849 and later named after him. For the origin of the term TV stone or television stone see section Properties.

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the ulexite belonged to the common mineral class of "carbonates, nitrates and borates" and to the department of "group borates", where it was the only member of the unnamed group V / H. 14 made.

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns ulexite to the now independent class of "borates" and there in the department of "pentaborates". This is further subdivided according to the structure of the borate complexes, so that the mineral can be found according to its structure in the subdivision "Island Pentaborate (Neso-Pentaborate)", where it forms the unnamed group 6.EA.25 as the only member .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , classifies ulexite as the outdated Strunz system in the class of "carbonates, nitrates and borates" and there in the section and subdivision of the same name for "water-containing borates with hydroxyl or halogen" . Here he can also be found as the only member of the unnamed group 05/26/11 .

Crystal structure

Ulexite crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a = 8.82  Å ; b = 12.87 Å; c = 6.68 Å; α = 90.4 °; β = 109.0 ° and γ = 105.0 ° as well as two formula units per unit cell . Template: room group / 2

properties

Ulexit, representation of the image guide effect

If the surface is fibrous and smoothly ground perpendicular to the fiber, the mineral is able to project underlaid text or images onto the stone surface. Because of this property, the ulexite is also known as television stone , television stone or TV stone for short .

Under UV light , some ulexites show a yellow to greenish yellow or creamy white, possibly also blue fluorescence . With a Mohs hardness of 2 to 2.5, ulexite is very soft (can still be scratched with a fingernail), but it is also very brittle and can be completely split parallel to the fibers.

Education and Locations

Needle-shaped ulexite crystals with superimposed, partially granular calcite crystals from Boron , Kern County , California, USA (size: 4.4 cm × 3.8 cm × 2.2 cm)

Ulexite forms in sediment in drying borax or salt lakes or salt marshes . If condensation nuclei are present, the mineral crystallizes out of the solution in a preferred growth direction. Accompanying minerals are other borate minerals.

Locations include Jujuy and Salta in Argentina; Potosí Department in Bolivia; New Brunswick , Newfoundland and Labrador and Nova Scotia in Canada; at Antofagasta , Coquimbo and in the Tarapacá region in Chile; Qinghai and the Tibet Autonomous Region in China; Hessen , Saarland and Thuringia in Germany; Zanjan in Iran; Atyrau in Kazakhstan; Arequipa in Peru; Serbia ; Kütahya , Central Anatolia and the Marmara Region in Turkey; as well as California , Nevada and Oklahoma in the United States .

use

Ulexite is an important ore for the extraction of boron.

Fibrous varieties of pure white color are processed into gemstones that are cabochon- cut and show the coveted cat-eye effect. However, the mineral is very sensitive to any influence of heat. Even hot water can cause noticeable damage. The same applies to cleaning treatments with alkalis , acids , galvanic baths and ultrasound.

See also

literature

  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 589 (first edition: 1891).
  • Subrata Ghose, Che'ng Wan, Joan R. Clark: Ulexite, NaCaB 5 O 6 (OH) 6 · 5H 2 O: structure refinement, polyanion configuration, hydrogen bonding, and fiber optics . In: American Mineralogist . tape 63 , 1978, pp. 160–171 ( rruff.info [PDF; 1.3 MB ]).
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 133 .

Web links

Commons : Ulexite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  350 .
  2. ↑ Webmineral - Ulexite (English)
  3. ↑ a b c Ulexite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001. ( PDF 67.8 kB )
  4. ↑ a b c d e Mindat - Ulexite (English)
  5. ^ Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 218 .
  6. ↑ Find location list for ulexite at the Mineralienatlas and at Mindat
  7. ↑ Ulexite. In: Leopold Rössler: Gemstone Knigge.