Metavariscite

Metavariscite
	Metavariscite from Lucin, Pilot Range, Box Elder Country, Utah , United States
General and classification
other names	Clinovariscit
chemical formula	Al [PO 4 ] • 2H 2 O
Mineral class; (and possibly department)	Phosphates, arsenates and vanadates
System no. to Strunz ; and to Dana	8th CD.05 ( 8th edition : VII / C.09) ; 04/40/03/01
Similar minerals	Phosphosiderite (iron analogue)
Crystallographic Data
Crystal system	Monoclinic
Crystal class ; symbol	monoclinic prismatic; 2 / m
Space group	P 2 1 / n (No. 14, position 2)
Lattice parameters	a = 5.178 Å ; b = 9.514 Å; c = 8.454 Å ; β = 90.35 °
Formula units	Z = 4
Twinning	Contact twins at {102}
Physical Properties
Mohs hardness	3.5
Density (g / cm 3 )	measured: 2.51 to 2.54; calculated: 2.535
Cleavage	To {010}
colour	bright green, colorless in reflected light
Line color	White
transparency	transparent to translucent
shine	Glass gloss
Crystal optics
Refractive indices	n α = 1.551 ; n β = 1.558 ; n γ = 1.582
Birefringence	δ = 0.031
Optical character	biaxial positive
Axis angle	2V = 55 °
Pleochroism	weak; X = colorless; Y = Z = light green
Other properties
Chemical behavior	soluble in hydrochloric acid after heating, soluble in alkalis

Metavariscite is a rare mineral from the mineral class of phosphates , arsenates and vanadates . It crystallizes in the monoclinic crystal system with the chemical composition Al [PO ₄ ] · 2H ₂ O, so it is aluminum orthophosphate containing water of crystallization .

Metavariscite forms pseudo- rhombic crystals , which consist of the crystal faces {010}, {011}, {130} and {110}. It also develops tabular crystals or spheroidal mineral aggregates . Contact twins after {102} can occur. The crystals are transparent to translucent and colored in a light green, they also have a glass-like sheen . A weak pleochroism makes the crystals appear colorless in the X-direction.

Metavariscite is one of the soft minerals because of its low Mohs hardness of 3.5.

Etymology and history

Metavariscite was first described as variscite . It was not until 1925 that Waltemar T. Schaller and Esper S. Larsen discovered that the refraction values differed slightly. They subsequently described Metavariscite after a sample from Utah , USA . At first they came up with an orthorhombic structure as well. In 1966 he discovered Par J. Borensztajn during a more extensive investigation of the metavariscite group and the variscite group that the metavariscite group, and thus also the metavariscite, crystallizes monoclinically.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the metavariscite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "water-containing phosphates without foreign anions", where together with Kolbeckit , Koninckit , Malhmoodit , Mansfieldit , Paraskorodit , Phosphosiderit , scorodite , strengite , variscite and Yanomamit the Variscit group with the system number VII / C.09 formed.

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and is used by the IMA, also assigns the metavariscite to the category of “phosphates etc. without additional anions; with H ₂ O “. However, this is further subdivided according to the size of the cations and the amount of crystal water, so that the mineral is classified according to its composition in the sub-section “with only medium-sized cations; RO ₄ : H ₂ O = 1: 2 “can be found where it is with Kolbeckite and Phosphosiderite in the Metavariscite group named after him with the system number 8.CD.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the metavariscite to the class of "phosphates, arsenates and vanadates" and there in the section "water-containing phosphates etc." (No. 40) and there in the sub-group "water-containing phosphates etc., with A ³⁺ XO ₄ × x (H ₂ O) “. Here it can also be found together with Kolbeckite and Metavariscite in the Metavariscite group named after it with the system number 40.04.03 .

Crystal structure

Metavariscite crystallizes isotypically to phosphosiderite monoclinically in the space group P 2 ₁ / n (space group no. 14, position 2) with the lattice parameters a = 5.178 Å , b = 9.514 Å, c = 8.454 Å and ß = 90.35 ° as well as four Formula units per unit cell . Template: room group / 14.2

The [PO ₄ ] ³⁻ units, i.e. the phosphate groups, form tetrahedral units. All oxygen atoms are also bound to aluminum atoms, which are four-fold coordinated. In theory, both the phosphorus and the aluminum would now be in the +4 oxidation state, in reality the phosphorus is in the +5 oxidation state, while the aluminum is in the +3 oxidation state.

Modifications and varieties

There is also an anhydrous form of metavariscite as a mineral, it is called berlinite . In addition, Metavariscite is dimorphic ; Variscite exists as an orthorhombic form.

Metavariscite is the aluminum analogue of phosphosiderite , an iron (III) phosphate also with two water of crystallization atoms.

Education and Locations

Metavariscite occurs as a secondary mineral to triphyline in pegmatite rocks . It is communalized with triphyline, barbosalite , leukophosphite , laueit , hureaulite , strictite and turquoise .

About 20 sites are known of Metavariscite.

Two sites are known in Germany . The first is in Lower Saxony in the Harz region , more precisely in Clausthal-Zellerfeld in Oberschulenberg . The other is in Thuringia near Gera , in Ronneburg .

In Austria , a location has been discovered. It is located in Lower Austria in Trandorf , Waldviertel .

Further occurrences in Europe can be found in the Spanish regions of Catalonia and Navarra , in the Polish Voivodeship Świętokrzyskie and in the Czech region of Bohemia .

Other locations can be found in Australia , Bolivia , Colombia , South Africa and the US states of Arkansas , Idaho , Nevada , Utah (where the type locality is) and Wisconsin .

literature

R. Kniep, D. Mootz: Metavariscite - A redetermination of its crystal structure . In: Acta Crystallographica, Section B . tape 29 , 1973, doi : 10.1107 / S0567740873006503 .
Commission on new minerals and mineral names . In: International Mineralogical Association (Ed.): Mineralogical Magazine . tape 36 , 1980, pp. 1053-1055 ( rruff.info [PDF]). Metavariscite on page 1053
XueJiao Tang, Maria J. Gentiletti, Abdessadek Lachgar: Synthesis and crystal structure of indium arsenate and phosphate dihydrates with variscite and metavariscite structure types . In: Journal of Chemical Crystallography . tape 31 , 2001, p. 45-50 , doi : 10.1023 / A: 1013778603055 .
Ray L. Frost, Matt L. Weier, Kristy L. Erickson, Onuma Carmody, Stuart J. Mills: Raman spectroscopy of phosphates of the variscite mineral group . In: Journal of Chemical Crystallography . tape 35 , issue 12, 2004, p. 1047-1055 , doi : 10.1002 / jrs.1251 .
Georges Calas, Laurence Galoisy, Amonmat Kiratisin: The origin of the green color of variscite . In: American Mineralogist . tape 90 , 2005, pp. 984–990 ( rruff.info [PDF; 189 kB ]).

Web links

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

Database-of-Raman-spectroscopy - Metavariscite (database, also contains further literature)
American-Mineralogist-Crystal-Structure-Database - Metavariscite (database for crystal structure data)

Individual evidence

↑ ^a ^b ^c Mineral Atlas: Metavariscite
↑ ^a ^b ^c ^d ^e ^f Phosphosiderite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy . Mineralogical Society of America, 2001 ( handbookofmineralogy.org [PDF]).
^ Mindat - Metavariscite
^ Esper J. Larsen, Waldemar T. Schaller: The identity of variscite and peganite and the dimorphous form, metavariscite . In: American Mineralogist . tape 10 . Mineralogical Society of America, 1925, pp. 23–28 ( rruff.info [PDF]).
^ Par J. Borensztajn: Structures cristallines de la métavariscite et de la métastrengite . In: Bulletin de la Société Française de Minéralogie et de Cristallographie . tape 89 , 1966, pp. 428-438 ( rruff.info [PDF]).
^ Paul B. Moore: The crystal structure of metastrengite and it's relationship to strengit and phosphophyllite . In: American Mineralogist . tape 51 . Mineralogical Society of America, 1966 ( minsocam.org [PDF]).
↑ Number of locations in Mindat
↑ Find location list for Metavariscite at the Mineralienatlas and at Mindat

[Mineralienatlas-1] Mineral Atlas: Metavariscite

[Datenblatt-2] ↑ ^a ^b ^c ^d ^e ^f Phosphosiderite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy . Mineralogical Society of America, 2001 ( handbookofmineralogy.org [PDF]).

[Mindat-3] Mindat - Metavariscite

[SchallerLarsen-4] Esper J. Larsen, Waldemar T. Schaller: The identity of variscite and peganite and the dimorphous form, metavariscite . In: American Mineralogist . tape 10 . Mineralogical Society of America, 1925, pp. 23–28 ( rruff.info [PDF]).

[Borensztajn-5] Par J. Borensztajn: Structures cristallines de la métavariscite et de la métastrengite . In: Bulletin de la Société Française de Minéralogie et de Cristallographie . tape 89 , 1966, pp. 428-438 ( rruff.info [PDF]).

[Moore-6] Paul B. Moore: The crystal structure of metastrengite and it's relationship to strengit and phosphophyllite . In: American Mineralogist . tape 51 . Mineralogical Society of America, 1966 ( minsocam.org [PDF]).

[Anzahl_Fundorte-7] Number of locations in Mindat

[Fundorte-8] Find location list for Metavariscite at the Mineralienatlas and at Mindat