Admontite

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Admontite
General and classification
other names

IMA 1978-012

chemical formula
  • MgB 6 O 10 • 7H 2 O
  • Mg [B 6 O 10 ] • 7H 2 O
  • Mg [B 6 O 7 (OH) 6 ] • 4.5H 2 O
Mineral class
(and possibly department) 		Borates (formerly carbonates, nitrates and borates)
System no. to Strunz
and to Dana 		6.FA.15
26.06.03.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / c (No. 14)Template: room group / 14
Lattice parameters a  = 12.66  Å ; b  = 10.09 Å; c  = 11.32 Å
β  = 109.6 °
Formula units Z  = 4
Physical Properties
Mohs hardness 2 to 3
Density (g / cm 3 ) measured: 1.82; calculated: 1.831
Cleavage is missing
Break ; Tenacity shell-like
colour colorless
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.442
n γ  = 1.504
Birefringence δ = 0.062
Optical character biaxial negative
Axis angle 2V = ≈ 30 °
Other properties
Chemical behavior slowly decomposes in water

Admontite is a very rare mineral from the mineral class of " borates " with the chemical composition MgB 6 O 10 · 7H 2 O or in the crystal-chemical structural formula notation according to Strunz, Mg [B 6 O 10 ] · 7H 2 O. Admontite is thus chemically seen a hydrous magnesium borate.

Admontite crystallizes in the monoclinic crystal system and develops only slightly pronounced or corroded crystals up to about one millimeter in size, which are stretched along the c-axis. The crystals are generally colorless and transparent with a glass-like sheen on the surfaces. Due to multiple refraction due to lattice defects or polycrystalline formation, these can also appear white

With a Mohs hardness of 2 to 3, admontite is one of the soft minerals that, like the reference minerals gypsum (2) and calcite (3), can either be scratched with a fingernail or with a copper coin.

Etymology and history

Admontite was recently discovered along with three other boron-containing minerals for the first time in the open pit "curtain wall", a to 1980 mined gypsum - and anhydrite - deposit at Admont in the Austrian province of Styria discovered. As early as 1976, the minerals were briefly described by Kurt Walenta , but without naming them, because due to the difficult chemical analysis not all the necessary data for a complete description were available.

After the chemical composition of Admontit could be clarified, Walenta submitted his test results and the name chosen according to its type locality for examination at the International Mineralogical Association (IMA) (internal entry number of the IMA: 1978-012). After being recognized as an independent mineral species, the first description was published the following year in the specialist magazine Tschermaks Mineralogische und Petrographische Mitteilungen (TMPM).

classification

Since Admontite was only recognized as an independent mineral in 1978, it is not yet listed in the 8th edition of the Strunz mineral classification, which has been outdated since 1977 . Only in the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , was the mineral given the system and mineral number. V / H.17-10 . In the "Lapis Classification" this represents the class of the "nitrates, carbonates and borates" and then the "Group borates" department where admontite with Aksait , Mcallisterit and Rivadavit forms an independent but unnamed group (as of 2018).

The 9th edition of Strunz's mineral systematics, valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, assigns admontite to the independent class of “borates” and there to the department of “hexaborates”. This is further subdivided according to the crystal structure of the borate complex, so that the mineral can be found according to its structure in the sub-section "Island Hexaborate (Neso-Hexaborate)", where it is the only member of the unnamed group 6.FA.15 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the admontite like the lapis systematics to the common class of "carbonates, nitrates and borates", but there in the already more finely subdivided section and subdivision of the same name of " hydrous borates with hydroxyl or Halogen ”. Here he can be found as the only member of the unnamed group 06/26/03 .

Chemism

The idealized (theoretical) composition of admontite (MgB 6 O 10 · 7H 2 O) consists of 6.48% magnesium (Mg), 17.28% boron (B), 72.48% oxygen (O) and 3.76 % Hydrogen (H).

Crystal structure

Admontite crystallizes monoclinically in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 12.66  Å ; b  = 10.09 Å; c  = 11.32 Å and β = 109.6 ° as well as 4 formula units per unit cell . Template: room group / 14

The crystal structure of admontite consists of three three-membered B [3] B 2 [4] rings that are connected to one another via a central oxygen atom. 6-fold coordinated magnesium atoms link these structural units to form chains parallel to the c-axis.

properties

Admontite slowly decomposes in water. When heated, it loses part of its crystal water below 100 ° C, the rest between 150 and 350 ° C.

Education and Locations

Admontite forms in plaster - deposits and is there in accordance with this in paragenesis to find. Other accompanying minerals include anhydrite , eugsterite , hexahydrite , Löweit , pyrite and quartz .

So far (as of 2020) the mineral could only be detected at its type locality Schildmauer near Admont in Austria.

See also

literature

  • A. dal Negro, L. Ungaretti, R. Basso: The crystal structure of synthetic hydrated borates (II) MgO • 3B 2 O 3 · 7H 2 O . In: Crystal Structure Communications . tape 5 , 1976, p. 433-436 (English).
  • Kurt Walenta : Admontite, a new borate mineral from the Schildmauer gypsum deposit near Admont in Styria (Austria) . In: TMPM Tschermaks Mineralogische und Petrographische Mitteilungen . tape 26 , no. 1-2 , 1979, pp. 69-77 , doi : 10.1007 / BF01081292 , bibcode : 1979TMPM ... 26 ... 69W .
  • Michael Fleischer , Adolf Pabst , Joseph Anthony Mandarino : New mineral names . In: American Mineralogist . tape 65 , 1980, pp. 205–210 (English, rruff.info [PDF; 1,2 MB ; accessed on January 10, 2020]).
  • Kurt Walenta: On the chemistry of Admontit and Makhachkiit . In: Swiss mineralogical and petrographic messages . tape 62 , 1982, pp. 177–183 ( available online at e-periodica.ch [accessed January 10, 2020]).

Web links

Individual evidence

  1. ↑ a b c Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: November 2019. (PDF 1720 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, November 2019, accessed January 11, 2020 .
  2. ↑ a b c d e Stefan Weiss: The great Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  3. ↑ 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.  354 (English).
  4. ^ A b David Barthelmy: Admontite Mineral Data. In: webmineral.com. Retrieved January 10, 2020 .
  5. ↑ a b c d e f g Admontite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 67  kB ; accessed on January 11, 2020]).
  6. ↑ a b c Admontite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 11, 2020 .
  7. ^ A b Michael Fleischer , Adolf Pabst , Joseph Anthony Mandarino : New mineral names . In: American Mineralogist . tape  65 , 1980, pp. 205–210 (English, rruff.info [PDF; 1,2 MB ; accessed on January 10, 2020]).
  8. ↑ Type locality Schildmauer, Admont, Ennstaler Alpen, Styria, Austria. In: mindat.org. Hudson Institute of Mineralogy, accessed January 11, 2020 .
  9. ↑ Schildmauer opencast mine, Admont, Liezen district, Styria, Austria. In: Mineralienatlas Lexikon. Stefan Schorn u. a., accessed on January 11, 2020 .
  10. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1816 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed January 11, 2020 .
  11. ↑ List of locations for Admontite in the Mineralienatlas and Mindat , accessed on January 11, 2020.