Allanpringite

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Allanpringite
Allanpringite-122708.jpg
Allanpringit from the Mark pit near Essershausen not far from Weilburg, Hesse, Germany (field of view: 4 mm)
General and classification
other names

IMA 2004-050

chemical formula Fe 3 [(OH) 3 | (PO 4 ) 2 ] • 5H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.DC.50
42.10.02.02
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  = 9.777  Å ; b  = 7.358 Å; c  = 17.830 Å
β  = 92.19 °
Formula units Z  = 4
Frequent crystal faces {010} and various unidentifiable {hkl}
Twinning always, parallel [010]
Physical Properties
Mohs hardness ≈ 3
Density (g / cm 3 ) 2.54 (measured); 2.583 (calculated)
Cleavage excellent // for the morphological longitudinal extension, good // {010}
Break ; Tenacity uneven; brittle
colour pale brownish yellow
Line color white with a pale yellowish tinge
transparency translucent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.662
n β  = 1.675
n γ  = 1.747
Birefringence δ = 0.085
Optical character biaxial positive
Axis angle 2V = 48
Pleochroism strong from X = Y = colorless to Z = dark yellow

Allanpringite is a very seldom occurring mineral from the mineral class of " phosphates , arsenates and vanadates " with the chemical formula Fe 3 [(OH) 3 | (PO 4 ) 2 ] · 5H 2 O. The mineral is therefore, chemically speaking, a water-containing iron - Phosphate with additional hydroxide ions .

Allanpringite crystallizes in the monoclinic crystal system and exclusively develops needle-like crystals elongated according to [010] with a maximum length of 1.5 mm, which come together to subparallel, bundle-shaped aggregates of up to 2 mm in length.

Etymology and history

Allanpringit was found in 1999 on the dump of the small, long-abandoned “Mark” iron mine near Essershausen im Taunus by the mineral collector Michael Legner. Initial studies suggested a new, secondary iron phosphate. This could be analyzed and described as allanpringite in 2006 by a German-Austrian research team with Uwe Kolitsch, Heinz-Jürgen Bernhardt, Christian L. Lengauer, Günter Blass and Ekkehart Tillmanns. They named the mineral after the Australian mineralogist and curator at the South Australian Museum in Adelaide Allan Pring in recognition of his countless contributions to the “mineralogical rainforest”, especially of phosphates, arsenates and sulfosalts.

In 2004 the mineral was recognized by the International Mineralogical Association (IMA).

Type material of the mineral (holotype) is kept in the Natural History Museum Vienna in Austria (catalog no. ??).

classification

Since allanpringite was only recognized as an independent mineral in 2005, it is not listed in the Strunz mineral system (8th edition), which has been outdated since 2001 . Only in the “Lapis mineral directory”, which was last updated in 2014, which, out of consideration for private collectors and institutional collections, is still based on the classic system of Karl Hugo Strunz , was the mineral given system no. VII / D.13-15 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies allanpringite in the category of “phosphates etc. with additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the other anions to the phosphate, arsenate or vanadate complex, so that the mineral is classified in the sub-section “With only medium-sized cations; (OH etc.): RO 4  = 1: 1 and <2: 1 “can be found, where together with Wavellit it forms the Wavellite group 8.DC.50 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns allanpringite to the class of "phosphates, arsenates and vanadates" and there to the category of "anhydrous phosphates, etc., with hydroxyl or halogen". Here it can be found together with Wavellite in Wavellite Group 42.10.02 within subdivision 42.10 Phosphates containing water etc., with hydroxyl or halogen with (AB) 3 (XO 4 ) 2 Z q × x (H 2 O) .

Crystal structure

Allanpringite crystallizes in the monoclinic crystal system in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 9.777  Å ; b  = 7.358 Å; c  = 17.830 Å and β = 92.19 ° as well as four formula units per unit cell . Template: room group / 14

The crystal structure of allanpringite is a monoclinically disturbed, pseudo-orthorhombic variant of the Al analogue wavellite. Chains of disturbed Fe (O, OH, H 2 O) 6 - octahedra parallel [010] with PO 4 - tetrahedra with common corners linked via common oxygen atoms. A positionally separated water molecule sits in the channels created in this way, which are also laid out parallel [010]. The average Fe-O distances of the three non-equivalent Fe atoms vary between 2.014 and 2.021 Å. Single crystal laser Raman spectroscopy confirms an all-encompassing weak system with hydrogen bonds . The structure of allanpringite is related to the crystal structures of kingite and mitryaevaite .

properties

morphology

Allanpringite occurs in the form of [010] elongated, needle-like, always twinned crystals with a maximum length of 1.5 mm, which form sub-parallel, bundle-shaped aggregates of up to 2 mm in length. The only crystal form that can be identified is {010}. Due to the formation of twins and the sub-parallel intergrowth of the individual crystals, the prisms cannot be indexed. The terminating head surfaces of the crystals are rounded and probably consist of several different {hkl} shapes.

physical and chemical properties

The crystals of allanpringite are pale brown-yellow, the line color of the mineral is described as white with a pale yellowish tinge. The surfaces of the allanpringite crystals have a glass-like sheen .

Due to its brittleness, the mineral breaks in a similar way to glass or quartz , with the edges of the break being uneven. With a Mohs hardness of ≈ 3, allanpringite is one of the medium-hard minerals that, like the reference mineral calcite, can be scratched with a copper coin. The calculated density of the mineral is 2.583 g / cm 3 . The mineral has two cleavages . On the one hand it splits excellently parallel to the morphological longitudinal extent, on the other hand it splits well parallel to {010}.

Modifications and varieties

Allanpringite is the monoclinic, pseudoorthorhombic, Fe 3+ -dominant analogue of the orthorhombic, Al-dominated wavellite, with which it does not form a mixed crystal row. Allanpringite has almost the same chemical composition as the amorphous santabarbaraite . It can be viewed as its polymorph , but has a completely different genesis. The extreme rarity of allanpringite in nature suggests that the mineral either has only a very small stability field or is only a metastable phase.

Education and Locations

Allanpringite is found on the dump of a former iron ore deposit, the dominant ore mineral of which was "Limonite" (mainly grape-grape goethite). It is accompanied by beraunite in the form of the reddish variety "Oxiberaunit", kakoxes in divergent-rayed aggregates, hemispheres and felt-like coatings, strictite in white, opaque spheres and solid, earthy cryptomelan . From paragenesis it can be deduced that allanpringite is either a supergenic mineral or represents a hydrothermal low temperature formation.

So far (as of 2016) the mineral could only be found at its type locality , the abandoned iron mine “Mark” near Essershausen, Hesse , Germany , 5 km southeast of Weilburg .

use

Allanpringite is only of interest to collectors due to its rarity.

See also

literature

  • Uwe Kolitsch, Heinz-Jürgen Bernhardt, Christian L. Lengauer, Günter Blass and Ekkehart Tillmanns (2006): Allanpringite, Fe 3 (PO 4 ) 2 (OH) 3 5H 2 O, a new ferric iron phosphate from Germany, and its close relation to wavellite. In: European Journal of Mineralogy , Volume 18, 793-801 ( PDF, 0.99 MB ).

Web links

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

Individual evidence

  1. ↑ a b c d e f g h i j Uwe Kolitsch, Heinz-Jürgen Bernhardt, Christian L. Lengauer, Günter Blass and Ekkehart Tillmanns (2006): Allanpringite, Fe 3 (PO 4 ) 2 (OH) 3 · 5H 2 O , a new ferric iron phosphate from Germany, and its close relation to wavellite. In: European Journal of Mineralogy , Volume 18, 793-801 ( PDF, 0.99 MB ).
  2. ↑ 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 .
  3. ↑ Mindat - Number of localities for Allanpringit
  4. ↑ Find location list for allanpringite in the Mineralienatlas and Mindat