Luneburgite

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Luneburgite
General and classification
chemical formula
  • Mg 3 [(PO 4 ) 2 | B 2 (OH) 6 ] • 6H 2 O
  • Mg 3 [B 2 (OH) 6 (PO 4 ) 2 ] • 6H 2 O
  • Mg 3 (H 2 O) 6 [B 2 (OH) 6 (PO 4 )]
Mineral class
(and possibly department) 		Borates (formerly carbonates, nitrates and borates)
System no. to Strunz
and to Dana 		6.AC.60 ( 8th edition : V / H.03)
05/43/11/01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 6.3475 (6)  Å ; b  = 9.8027 (II) Å; c  = 6.2976 (5) Å
α  = 84.46 (l) °; β  = 106.40 (l) °; γ  = 96.40 (1) °
Formula units Z  = 1
Twinning generally rotation twins according to [1 1 0]
Physical Properties
Mohs hardness ≈ 2
Density (g / cm 3 ) measured: 2.05; calculated: 2.204
Cleavage clearly after {010}
colour colorless, white to brownish white, green
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.520 to 1.522
n β  = 1.540 to 1.541
n γ  = 1.545 to 1.548
Birefringence δ = 0.025 to 0.026
Optical character biaxial negative
Axis angle 2V = 63 °

Lüneburgite is a rarely occurring mineral from the mineral class of " borates " (formerly carbonates, nitrates and borates ) with the chemical composition Mg 3 [(PO 4 ) 2 | B 2 (OH) 6 ] · 6H 2 O and is therefore chemically seen a magnesium - borophosphate .

Lüneburgite crystallizes in the triclinic crystal system , but rarely develops crystals visible with the naked eye and pseudo-hexagonal twins with a tabular to blocky habit up to about three millimeters in size. It is mostly found in the form of fine-grained to earthy tubers as well as kidney or spherical mineral aggregates . In its pure form, Lüneburgite is colorless. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a brownish-white or green color.

Etymology and history

Lüneburgite was first discovered in 1870 in the Lüneburg district of Volgershall in northeast Lower Saxony . The mineral was described by C. Nöllner, who named it after its type locality .

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , Lüneburgite still belonged to the common mineral class of "carbonates, nitrates and borates" and there to the department of "group borates", where together with Wiserit it was the "Wiserit-Lüneburgite- Group "with the system no. V / H.03 formed.

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 Lüneburgite to the now independent class of "borates" and there in the department of "monoborates". This is further subdivided according to the crystal structure , so that the mineral according to its structure in the sub-section “B (O, OH) 4 , with and without additional anions ; 1 (T), 1 (T) + OH etc. ”is to be found where it is the only member of the unnamed group 6.AC.60 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Lüneburgite, however, to the class of "phosphates, arsenates and vanadates" and there to the department of "phosphates". Here he is to be found as the only member in the unnamed group 43.05.11 within the sub-section “ Compound phosphates etc. (water-containing compound anions with hydroxyl or halogen)”.

Crystal structure

Lüneburgite crystallizes in the triclinic crystal system in the space group P 1 (space group  no.2 ) with the lattice parameters a = 6.3475 (6)  Å , b  = 9.8027 (ll) Å, c  = 6.2976 (5) Å, α = 84.46 (l) °, β = 106.40 (l) ° and γ = 96.40 (1) °, as well as one formula unit per unit cell .

Education and Locations

Lüneburgite forms in marine evaporites . So far, the mineral has only been found in a few places in anhydrite or gypsum .

In addition to its type locality Lüneburg (Lower Saxony) and the Thuringian Forest in Germany, Antofagasta in Chile are also found sites ; Serbia ; the Crimean peninsula in Ukraine; as well as New Mexico in the USA.

See also

literature

  • Wilhelm Biltz, E. Marcus: About the Lüneburgit. In: Journal of Inorganic Chemistry. Special reprint. Edited by G. Tamman and Richard Lorenz. Voss Leipzig 1912
  • C. Nöllner: Ueber den Lüneburgit In: Session reports of the Royal Bavarian Academy of Sciences in Munich. Volume 1, 1870, pp. 291–293 ( PDF 200 kB )
  • Jens Müller and Frank Fabricius: 27. Lüneburgite [Mg 3 (PO 4 ) 2 B 2 O (OH) 4 × 6H 2 O] in upper miocene sediments of the eastern mediterranean sea (available online at deepseadrilling.org ; PDF 815.1 kB)
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 587 (first edition: 1891).

Web links

Individual evidence

  1. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  2. ^ IMA / CNMNC List of Mineral Names; September 2016 (PDF 1.65 MB)
  3. ↑ a b c d PK Sen Gupta, GH Swihart, R. Dimitrijevic, MB Hossain: The crystal structure of luneburgite, Mg 3 (H 2 O) 6 [B 2 (OH) 6 (PO 4 ) 2 ] In: American Mineralogist Volume 76, 1991, pp. 1400–1407 ( PDF 843.9 kB )
  4. ↑ Webmineral - Luneburgite (English)
  5. ↑ a b c d Lüneburgite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 489 kB )
  6. ↑ a b c d e Mindat - Lüneburgite (English)
  7. ↑ Find location list for Lüneburgite at the Mineralienatlas and at Mindat