Prosperite

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Prosperite
General and classification
other names

IMA 1978-028

chemical formula
  • Ca 2 Zn 4 [H 2 O | (AsO 4 ) 4 ]
  • Ca 2 Zn 4 (AsO 4 ) 4 · H 2 O
  • CaZn 2 H [OH | (AsO 4 ) 2 ]
  • HCaZn 2 (AsO 4 ) 2 (OH)
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.CA.60 ( 8th edition : VII / B.23)
02/40/04/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 19.238  Å ; b  = 7.731 Å; c  = 9.765 Å
β  = 104.47 °
Formula units Z  = 4
Frequent crystal faces {100}, { 1 01}, {110}, { 1 11}, {421}, {540}, {210}, {310}, {301}, { 1 12}
Physical Properties
Mohs hardness 4.5
Density (g / cm 3 ) 4.31 (measured); 4.40 (calculated)
Cleavage no
Break ; Tenacity not specified; not specified
colour white to colorless (aggregates slightly bluish)
Line color White
transparency translucent
shine strong glass to silk gloss
Crystal optics
Refractive indices n α  = 1.746
n β  = 1.748
n γ  = 1.768
Birefringence δ = 0.022
Optical character biaxial positive
Axis angle 2V = 34 ° (observed), 36 ° (calculated)

Prosperite is a very rare mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the chemical formula Ca 2 Zn 4 [H 2 O | (AsO 4 ) 4 ] and is therefore chemically a water-containing calcium - zinc arsenate.

Prosperite forms prismatic crystals, stretched in the direction of the c-axis, up to one centimeter long and one millimeter in diameter, which come together to form radial aggregates and sub-parallel to sheaf-shaped formations. The mineral was found along with konichalcite , adamin and copper-bearing austinite in cavities in massive chalcosine in the Tsumeb Mine , Namibia.

Etymology and history

Prosper John Williams is considered the discoverer of Prosperite , who gave the unknown mineral to the Royal Ontario Museum in Toronto for identification in 1976. Corresponding investigations led to the determination of the presence of a new mineral, which was recognized in 1978 by the International Mineralogical Association (IMA) under the number "IMA 1978-028" and in 2001 by Robert Irwin Gait and Bozidar Darko Sturman from the Royal Ontario Museum in Toronto , Canada as well Pete J. Dunn of the National Museum of Natural History , Washington, DC , has been described as prosperite in the science magazine The Canadian Mineralogist. The mineral was named after the Canadian mineral dealer Prosper John Williams (1910–?) From Toronto, whose activities led to the enrichment of the Tsumeb collections of many museums, universities and private collectors around the world. The crystal structure determination carried out at the University of Stuttgart in 1982 led to a revision of the chemical formula.

Type material of the mineral is in the collection of the Smithsonian Institution belonging to National Museum of Natural History , Washington, DC (Collection no. 143732 (holotype) 143733), the Natural History Museum , London (Collection no. BM 1982.72 (Cotyp) and BM 1978,19), at the Royal Ontario Museum, Toronto, (collection no. M35388 (Cotyp), M35389, M35391) and in the archive of the University of Stuttgart in the "Mineralogical Collection of Professor Keller" (register no ST-78.28 at location 0/824-s27 / 2, part of the cotype, crystal used to determine the crystal structure).

classification

Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the prosperite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "anhydrous phosphates with foreign anions ", where together with Mélonjosephit it was an independent group VII / B.23 formed.

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 the prosperite to the category of “phosphates etc. without additional anions; with H 2 O “. This, however, is further divided according to the relative size of the participating cations , so that the mineral according to its composition in the subsection "With large and small / medium-sized cations" is to find where it is the only member of the unnamed group 8.CA.60 forms .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the prosperite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here he is to be found as the only member of the unnamed group 02/40/04 within the subdivision " Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O) ".

Chemism

Microprobe analyzes on Prosperit showed mean values ​​of 13.02% CaO; 33.22% ZnO; 1.35% CuO; 47.92% As 2 O 5 and 4.0% H 2 O. On the basis of 9 oxygen atoms , the empirical formula Ca 1.09 (Zn 1.91 Cu 0.08 ) Σ = 1.99 (As 0.98 O 3.98 ) 2 · 1.04H 2 O, which was idealized to HCaZn 2 (AsO 4 ) 2 (OH) and later to Ca 2 Zn 4 (AsO 4 ) 4 · H 2 O. The latter formula requires a CaO content of 12.01%; 34.88% ZnO; 49.25% As 2 O 5 and 3.86% H 2 O.

Crystal structure

Prosperite crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 19.238  Å ; b  = 7.731 Å; c  = 9.765 Å and β  = 104.47 Å as well as four formula units per unit cell . Template: room group / 15

In the crystal structure of prosperite zinc has the coordination number 5 in two different forms, both of which can be described as trigonal dipyramids . The Zn (1) polyhedron is extraordinarily deformed according to the bond angle. The deformation of the Zn (2) polyhedron is comparatively small. Two Zn (2) O 5 polyhedra form double groups over one edge. Such double groups of edge-sharing, trigonal dipyramids also occur in the crystal structures of Adamin and the two isotypic minerals paradamin and tarbuttite . To the double groups of Zn (2) O 5 polyhedra is across a corner of each of a Zn (l) O 5 Linked polyhedra. In this way, zigzag-shaped quadruple islands are created from the coordination polyhedra of zinc.

The coordination of calcium is much more complicated. The best charge balance is obtained for the coordination number 9. The coordination polyhedron can best be described as a heavily distorted Archimedean antiprism with a flat pyramid placed on one of the square surfaces . The atoms of the base area lie within the error limits in one plane, but deviate very strongly from the ideal square arrangement and form a rather irregular rhomboid with a very short diagonal. Two Ca (H 2 O) O 8 polyhedra are linked to form a double group over a surface. The two crystallographically different AsO 4 - tetrahedra are deformed only slightly. The components described are linked in a variety of ways via surfaces, edges and corners to form a framework. Certain preferred directions cannot be identified, which is consistent with the lack of cleavage of the prosperite.

properties

morphology

Prosperite forms slender, [001] elongated and {100} prismatic crystals up to 1 cm in length and 1 mm in diameter, which are often bent and twisted. They come together to form radial aggregates and sub-parallel to sheaf-shaped formations; often some of the larger acicular prisms are composed of a series of smaller crystals in parallel intergrowth. The form that determines the costume is the pinacoid {100}. Furthermore, { 1 01}, {110}, { 1 11}, {421}, {540}, {210}, {310}, {301} and { 1 12} were observed (in order of decreasing importance) .

physical and chemical properties

Prosperite crystals are colorless or white, aggregates also show a faint bluish tinge. The line color of the prosperits, on the other hand, is always white. The surfaces of the translucent crystals show a strong glass- to silk-like sheen . Prosperit has high light and medium double refraction (δ = 0.022).

No cleavage was found in the prosperite crystals, and no information on breakage or tenacity was found . The mineral has a Mohs hardness of 4.5 and is therefore one of the medium-hard minerals that are somewhat easier to scratch with a pocket knife than the reference mineral apatite (hardness 5). The measured density for prosperite is 4.31 g / cm³, the calculated density is 4.40 g / cm³.

Education and Locations

As a very rare mineral formation, prosperite could only be described from one point of discovery so far (as of 2016). Its type locality is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto Region , Namibia . The exact discovery site, the type level within the "Tsumeb Mine" is not known, but further steps come with Prosperit from 31 soles .

Prosperite occurs as a typical secondary formation in corroded ores in the oxidation zone of a complex Cu-Pb-Zn deposit in carbonate rocks. Zinc and arsenic originate from the decomposition of primary sulphidic ore minerals such as sphalerite and tennantite , calcium from the carbonate host rock . The prosperite crystals sit in cavities of altered chalcosine, which carries tiny drops of native silver , which contains approx. 20-25% by weight of mercury . At the type level, two types of cavities can be distinguished: one type is lined with tiny grass- to olive-green konichalcite crystals and, in addition to the prosperite, contains rosette-shaped aggregates of pale blue-green adamin crystals, while the other type is pale green, copper-containing austinite (40 mol% Contains konichalcite), prosperite and adamin. The age sequence of the minerals at the type level can be specified with primary sulfide → Konichalcite and Austinite → Adamin → Prosperite. Only later were polycrystalline coatings and maximum 1 mm crystals on prosperite, adamin and austinite identified as another new mineral, gaitite .

A second, later find on the 31st floor of the "Tsumeb Mine" yielded colorless to white, individually grown prosperite crystals up to 1 mm in size, accompanied by konichalcite, Austinite, barite and quartz . In addition, in 1981, during the first description of O'Danielite, sitting in corroded ores with chalcosin and tennantite from the "Tsumeb Mine", colorless prosperite was also found in its paragenesis , accompanied by pale pink colored coritnigite . Other accompanying minerals of prosperite mentioned in the literature are stranskiite , lavendulan , köttigite and tsumcorite .

use

Because of its rarity, Prosperite is only of interest to mineral collectors.

See also

literature

  • Prosperit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 67 kB )
  • Robert I. Gait, B. Darko Sturman, Pete J. Dunn: Prosperite, HCaZn 2 (AsO 4 ) 2 (OH), a new mineral from Tsumeb, South West Africa (Namibia) . In: The Canadian Mineralogist . tape 17 , 1979, pp. 87-92 ( rruff.info [PDF; 709 kB ]).
  • Paul Keller, Heinz Riffel, Heinz Hess: The crystal structure of prosperite, Ca 2 Zn 4 [H 2 O | (AsO 4 ) 4 ] . In: Journal of Crystallography . 158 (Issue 1-2), 1982, pp. 33–42 , doi : 10.1524 / zkri.1982.158.1-2.33 ( rruff.info [PDF; 439 kB ]).

Web links

Individual evidence

  1. ↑ a b c d e f Paul Keller, Heinz Riffel, Heinz Hess: The crystal structure of Prosperite, Ca 2 Zn 4 [H 2 O | (AsO 4 ) 4 ] . In: Journal of Crystallography . 158 (Issue 1-2), 1982, pp. 33–42 , doi : 10.1524 / zkri.1982.158.1-2.33 ( rruff.info [PDF; 439 kB ]).
  2. ↑ a b c d e Prosperit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 67 kB )
  3. ↑ a b c d e f g Mindat - Prosperit
  4. ^ 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.  454 .
  5. ↑ a b c d e f g h i j k Robert I. Gait, B. Darko Sturman, Pete J. Dunn: Prosperite, HCaZn 2 (AsO 4 ) 2 (OH), a new mineral from Tsumeb, South West Africa ( Namibia) . In: The Canadian Mineralogist . tape 17 , 1979, pp. 87-92 ( rruff.info [PDF; 709 kB ]).
  6. ↑ Catalog of Type Mineral Specimens - P. (PDF 113 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 2019 .
  7. ↑ Typmineral catalog Germany - storage of the type material for Prosperit
  8. ↑ Mindat - Number of localities for Prosperit
  9. ↑ Find location list for Prosperite in the Mineralienatlas and in Mindat
  10. ↑ a b Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, p. 255 + 322 .
  11. ↑ B. Darko Sturman, Pete J. Dunn: Gaitite, H 2 Ca 2 Zn (AsO 4 ) 2 (OH) 2 , a new mineral from Tsumeb, Namibia . In: The Canadian Mineralogist . tape 18 , 1980, pp. 197–200 ( rruff.info [PDF; 947 kB ]).
  12. ^ Paul Keller, Heinz Hess, Pete J. Dunn, D. Newbury: O'Danielite, NaZn 3 H 2 (AsO 4 ) 3 , a new mineral from Tsumeb, Namibia . In: New yearbook for mineralogy, monthly books . 1981 (issue 4), 1981, p. 155-160 .
  13. ↑ Paul Keller: Tsumeb / Namibia - one of the most spectacular mineral discovery sites on earth . In: Lapis . 9 (issue 7/8), 1984, p. 13-63 .