Zinc roselite

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Zinc roselite
General and classification
other names
  • Zinc croselite
  • IMA 1985-055
chemical formula Ca 2 Zn (AsO 4 ) 2 · 2H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana 		8.CG.10 ( 8th edition : VII / C.17)
02/40/03/03
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  = 5.827  Å ; b  = 12.899 Å; c  = 5.646 Å
β  = 107.69 °
Formula units Z  = 2
Twinning often after (100)
Physical Properties
Mohs hardness ≈ 3
Density (g / cm 3 ) 3.75 (measured); 3.77 (calculated)
Cleavage very perfect after {010}, indicated after {001}
Break ; Tenacity not given; brittle
colour colorless to white
Line color not given, well know
transparency translucent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.703
n β  = 1.710
n γ  = 1.720
Birefringence δ = 0.017
Optical character biaxial negative
Axis angle 2V = 50 ° (measured); 2V = 57 ° (calculated)
Pleochroism not pleochroic
Other properties
Chemical behavior Soluble in HNO 3 , poorly soluble in oxalic acid, HCl, and H 2 SO 4 . Sensitive to alkalis.

Zinc roselite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the chemical composition Ca 2 Zn (AsO 4 ) 2 · 2H 2 O and is therefore chemically a water-containing calcium - zinc - arsenate .

At its type locality, zinc roselite develops slat-shaped crystals up to 3 cm in size, elongated according to [001] and strongly striped parallel [001] , which come together to form aggregates that have grown together subparallel . Typical are associations with quartz , ferrous and zinc-bearing dolomite , tsumcorite , hematite , siderite and anglesite or tsumcorite, stranskiite , Leiteit , quartz and tennantite . The type locality of the mineral is the Tsumeb Mine near Tsumeb , Oshikoto Region , Namibia .

Etymology and history

At the beginning of the 1980s, John Innes , chief mineralogist of the Tsumeb Corporation, was able to recover a number of rare minerals on the 32nd level, 1st subsole, in the W40 mine of the Tsumeb Mine in Tsumeb, Namibia, including Leiteit, Schneiderhöhnit , Ludlockite , Schaurteit , Stottit and Bartelkeit an initially unidentifiable mineral was found, which turned out to be a new mineral phase. After the tests necessary for characterization, the new mineral was submitted to the International Mineralogical Association (IMA), which recognized it in 1985. In 1986, it was by an international research team led by the German mineralogist Paul Keller and John Innes and Pete J. Dunn (as Zinkroselith in the German science magazine "New Yearbook of Mineralogy, Monatshefte" English Zincroselite ) described. The authors named the mineral because of its crystal-chemical relationship with Roselith and the dominance of zinc on the [VI] M 2+ position.

The type material for zinc roselite (holotype) is kept at the University of Stuttgart (location TM-85.55 / 0/824-s27 / 2) and in the National Museum of Natural History , Washington, DC (catalog no. 163340). A Cotype specimen from the collection of William W. Pinch, previously in the possession of John Innes, is in the collection of the RRUFF project under the number "RRUFF ID: R100192".

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , zinc roselite belonged to the department of “water-containing phosphates without foreign anions ”, where together with Fairfieldit it formed the “Fairfieldite-Roselith group” with system no. VII / C.17 and the other members brandtite , cassidyite , roselith-β , collinsite , gaitite , hillite , messelite , parabrandtite , roselith , talmessite and wendwilsonite .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns zinc roselite 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 water of crystallization , so that the mineral is classified in the sub-section “With large and medium-sized cations; RO 4  : H 2 O = 1: 1 ”can be found where, together with the eponymous Roselith, as well as Brandtite and Wendwilsonite, the“ Roselith Group ”with the system no. 8.CG.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns zinc roselite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here it is in the " Roselith subgroup (monoclinic: P 2 1 / c ) " with system no. 40.02.03 and the other members Brandtite, Manganlotharmeyerite , Roselith and Wendwilsonite can be found within the sub-section "Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O)".

Chemism

Microprobe analyzes on zinc roselite from the Tsumeb mine showed mean values ​​of 25.0% CaO; 0.4% MgO; 0.9% MnO; 0.2% FeO; 15.9% ZnO; 49.3% As 2 O 3 and 7.7% H 2 O, from which the empirical formula Ca 2.06 (Zn 0.09 Mn 0.06 Mg 0.05 Fe 0.01 ) Σ = 1.02 ( AsO 4 ) calculated 1.98 · 1.97H 2 , which can be idealized to Ca 2 Zn (AsO 4 ) 2 · 2H 2 O. This ideal formula requires levels of 24.41% CaO; 17.72% ZnO; 50.03% As 2 O 3 and 7.84% H 2 O.

Zinc roselite is the Zn 2+ -dominant analogue of Co 2+ -dominated roselite, Mg-dominated wendwilsonite and Mn 2+ -dominated brandtite. At least partial solid solution formation with roselith and wendwilsonite is considered possible.

Crystal structure

Zinc roselite crystallizes in the monoclinic crystal system in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 5.827  Å ; b  = 12.899 Å; c  = 5.646 Å and β = 107.69 ° as well as two formula units per unit cell . Template: room group / 14

The crystal structure of zinc roselite consists of [AsO 4 ] tetrahedra , centrosymmetrical [Zn (H 2 O) 2 O 4 ] octahedra and tetragonal antiprisms [Ca (H 2 O) O 7 ], all of which are severely distorted. In the [Ca (H 2 O) O 7 ] polyhedron , Ca has a regular [7 + 1] coordination with seven relatively similar Ca-O distances of 2.372 to 2.506 Å and a very long Ca – O2 bond distance of 3.099 Å on. The centrosymmetric [Zn (H 2 O) 2 O 4 ] octahedron is stretched in the direction of the tetragonal axis.

The [Zn (H 2 O) 2 O 4 ] polyhedra and the [AsO 4 ] tetrahedra are connected via common vertices to form [Zn (H 2 O) 2 (AsO 4 ) 2 ] 4− chains, which have similarities the chains of the Kröhnkit type. However, they can be expanded by incorporating the [Ca (H 2 O) O 7 ] polyhedra. The latter share common O1 – H 2 O5 and O1 – O2 edges with the [Zn (H 2 O) 2 O 4 ] polyhedra or [AsO 4 ] tetrahedra, where [Ca 2 Zn (H 2 O ) 2 O 8 (AsO 4 ) 2 ] 16− rods arise. The sliding plane c of the monoclinic zinc roselite forms slightly undulating networks of the composition [Ca (H 2 O) O 5 ] 8− , which are stacked alternately with the [Zn (H 2 O) 2 (AsO 4 ) 2 ] 4− chains, but are oriented parallel (100). The [Ca (H 2 O) O 7 ] polyhedra are connected to one another only via two edges (O1 – O1 and O2 – O2). In this way, chains with an accentuated zigzag shape are created parallel [100], which are further connected in direction [010] by two O4 corners and thus form a dense network. A very strong hydrogen bond has developed between adjacent rod layers that are oriented parallel (010) and are otherwise relatively weakly linked in the direction of the b-axis.

Zinc roselite is isotypic (isostructural) to roselite. It is also the monoclinic polymorph to the triclinic gaitit .

properties

morphology

At its type locality, zinc roselite develops subparallel fused aggregates of 12 × 5 × 4 mm in diameter, which form crystals up to 1.5 mm in size in cavities. The crystals are lath-shaped, stretched according to [001] and strongly streaked parallel to the c-axis. On the mostly (100) twinned crystals, only unspecific {hk0} and {hkl} forms could be determined due to the strong striations. Crystals up to 2 cm in length that were originally labeled as cerussite have been observed extremely rarely .

physical and chemical properties

The crystals of zinc roselite are colorless to white, their line color is not specified, but is probably white. The surfaces of the translucent to transparent crystals have a glass-like sheen , which agrees well with the values ​​for light refraction .  Medium to high values ​​for light refraction (n α = 1.703; n β  = 1.710; n γ  = 1.720) and for birefringence (δ = 0.017) were found on the crystals of zinc roselite .

The zinc roselite described as brittle has a very perfect cleavage according to {010} and an indicated cleavage according to {001}. With a Mohs hardness of ≈ 3, the mineral is one of the medium-hard minerals and, like the reference mineral calcite, can be scratched with a copper coin. The measured density for zinc roselite is 3.75 g / cm³, the calculated density is 3.77 g / cm³. The mineral is neither in the long term nor in the short wavelength UV light , a fluorescent .

Zinc roselite is soluble in nitric acid , HNO 3 . It is also sparingly soluble in oxalic acid , hydrochloric acid , HCl, and sulfuric acid , H 2 SO 4 . The mineral is very sensitive to concentrated alkalis such as caustic soda , NaOH, and potassium hydroxide , KOH.

Education and Locations

Zinkroselith is a typical secondary mineral , which is located in the oxidation zone of arsenic-rich polymetallic non-ferrous metal - deposits formed.

In the "Tsumeb Mine" the mineral was found on a step made of solid tennantite, which was penetrated by veins of solid and drusy white quartz. Other paragenesis minerals are zinc-bearing dolomite and tsumcorite. Claudetite and stranskiite were also detected at the type level, but in separate inclusions . The exact first location of the zinc roselite is the mining W40 on the 32nd level, 1st sub-level, in Tsumeb, Namibia.

As a very rare mineral formation, zinc roselite could only be described from two sources so far (status 2018). The type locality is the "Tsumeb Mine" near Tsumeb, Oshikoto region , Namibia . The second site in the world is the mining district of Bou Azzer near Taznakht (Tazenakht), Ouarzazate province in the Drâa-Tafilalet region in southern Morocco . Zinc roselite was identified here on a specimen probably found in Aghbar in 1987 in the form of tiny, colorless to white crystals that contain equivalent amounts of Zn, Co and Mg.

Occurrences of zinc roselite in Germany , Austria or Switzerland are therefore not known.

use

Due to its rarity, zinc roselite is only of interest to the mineral collector.

See also

literature

  • Paul Keller, John Innes, Pete J.Dunn: Zincroselite, Ca 2 Zn (AsO 4 ) 2 · 2H 2 O, a new mineral from Tsumeb, Namibia . In: New yearbook for mineralogy, monthly books . tape 1986 , no. 11 , 1986, pp. 523-527 .
  • Zincroselite . 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; 444 kB ; accessed on June 14, 2018]).

Web links

Individual evidence

  1. ↑ a b Type Mineral Catalog Germany - Storage of the type material for zinc roselite
  2. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah Paul Keller, John Innes, Pete J. Dunn: Zincroselite, Ca 2 Zn (AsO 4 ) 2 · 2H 2 O, a new mineral from Tsumeb, Namibia . In: New yearbook for mineralogy, monthly books . tape 1986 , no. 11 , 1986, pp. 523-527 .
  3. ^ A b c d Paul Keller, Falk Lissner, Thomas Schleid: The crystal structures of zinc roselite and gaitite: Two natural polymorphs of Ca 2 Zn [AsO 4 ] 2 · 2H 2 O from Tsumeb, Namibia . In: European Journal of Mineralogy . tape 16 , no. 2 , 2004, p. 353-359 , doi : 10.1127 / 0935-1221 / 2004 / 0016-0353 .
  4. ↑ a b c d Paul Keller, John Innes: New minerals from Tsumeb . In: Lapis . tape 11 , no. 9 , 1986, pp. 28-32 .
  5. ↑ a b Mindat - Zincroselite (English)
  6. ↑ a b c Rudolf Duthaler, Stefan Weiß: Clean, prepare and store minerals. The workbook for the collector . 1st edition. Christian Weise Verlag, Munich 2008, ISBN 978-3-921656-70-9 , p. 150, 158, 187 .
  7. ↑ a b c Zincroselite . 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; 444  kB ; accessed on June 14, 2018]).
  8. ↑ a b Tsumeb.com - Zincroselite (English)
  9. ↑ Homepage of William W. Pinch: Zincroselite (English)
  10. ↑ RRUFF project: RRUFF - Zincroselite (English)
  11. ↑ a b Georges Favreau, Jacques Emile Dietrich: The minerals of Bou Azzer . In: Lapis . tape 31 , no. 7–8 , 2006, pp. 63 .
  12. ↑ a b Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, ISBN 3-925322-03-5 , pp. 255 .
  13. ↑ Mindat - Number of localities for zinc roselite
  14. ↑ a b List of locations for zinc roselite in the Mineralienatlas and Mindat