Dittmarit

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Dittmarit
General and classification
chemical formula NH 4 Mg [PO 4 ] • H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana 		8.CH.20 ( 8th edition : VII / C.23)
01/40/02/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol rhombic-pyramidal; mm 2
Room group (no.) Pmn 2 1 (No. 31)
Lattice parameters a  = 5.61  Å ; b  = 8.76 Å; c  = 4.79 Å
Formula units Z  = 2
Physical Properties
Mohs hardness "low"
Density (g / cm 3 ) measured: 2.15; calculated: 2.19
Cleavage Please complete!
colour colorless
Line color Please complete!
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.549
n β  = 1.569
n γ  = 1.571
Birefringence δ = 0.022
Optical character biaxial negative
Axis angle 2V = 40 ° (measured); 34 ° (calculated)

Dittmarit is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the orthorhombic crystal system with the composition NH 4 Mg [PO 4 ] · H 2 O, so it is chemically a water-containing ammonium magnesium phosphate .

Dittmarit only forms small, colorless and transparent crystals with shiny glass surfaces.

Etymology and history

Dittmarit was first discovered in the lava cave known as "Skipton Caves" near Skipton in the Australian administrative area Corangamite Shire (Victoria) and described in 1887 by MacIvor, who named the mineral after the German-British chemist Wilhelm Dittmar .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Dittmarit belonged to the general department of "Water-containing phosphates without foreign anions", where together with Hannayit , Mundrabillait , Niahit , Schertelit , Stercorit , Struvit , Struvit-K and Swaknoit formed the unnamed group VII / C.23 .

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also assigns the Dittmarit to the category of “phosphates etc. without 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 phosphate, arsenate or vanadate complex (RO 4 ) to crystal water (H 2 O), so that the mineral can be classified in the sub-section “With large and medium-sized cations; RO 4  : H 2 O <1: 1 “can be found, where it only forms the unnamed group 8.CH.20 together with Niahit .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Dittmarit to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here he can be found together with Niahit in the unnamed group 40.01.02 within the subdivision of " Water-containing phosphates etc., with A 2+ B 2+ (XO 4 ) × x (H 2 O) ".

Education and Locations

Dittmarit forms in dry bat guano and is accordingly found in caves inhabited by bats. As Begleitminerale occur among other Arcanit , Hannayit , Mundrabillait , Newberyit , Schertelit , Swaknoit and struvite.

Apart from its type locality "Skipton Caves" in Victoria, Australia, the mineral could so far (as of 2012) only in the Gcwihaba cave near Maun in Botswana, near Punta Patache about 8 km south of Puerto Patillos and 65 km south of Iquique in Chile and in the Arnhem Cave near Windhoek in Namibia.

Crystal structure

Dittmarit crystallizes orthorhombically in the space group Pmn 2 1 (space group no. 31) with the lattice parameters a  = 5.61  Å ; b  = 8.76 Å and c  = 4.79 Å and 2 formula units per unit cell .

See also

Web links

Individual evidence

  1. ↑ a b c d e 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.  487 .
  2. ↑ Webmineral - Dittmarite
  3. ↑ a b Dittmarite , in: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 63.4 kB )
  4. ↑ a b c d Mindat - Dittmarite