Ahlfeldite

from Wikipedia, the free encyclopedia
Ahlfeldite
Alfredopetrovite, Ahlfeldite & Chalcomenite.jpg
Ahlfeldite (pink) with chalcomenite (blue) and alfredopetrovite (colorless to gray) from the El Dragón mine, Antonio Quijarro province , Potosi, Bolivia
(size: 1.3 cm × 0.7 cm × 0.8 cm)
General and classification
other names
  • Nickel seleniate
chemical formula
  • Ni (SeO 3 ) • 2H 2 O
  • (Ni, Co) [SeO 3 ] • 2H 2 O
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.JH.10 ( 8th edition : IV / G.02b)
02.34.03.03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / n (No. 14, position 2)Template: room group / 14.2
Lattice parameters a  = 7.52  Å ; b  = 8.75 Å; c  = 6.44 Å
β  = 99.0 °
Formula units Z  = 4
Frequent crystal faces {110}, {011}, {032}, {103}, { 1 01}
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) measured: 3.37 (2); calculated: 3.51
Cleavage good after {110} and {103}
Break ; Tenacity brittle
colour light green, apple green, olive green, brown, brownish pink
Line color pale green to white
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.709
n β  = 1.752
n γ  = 1.787
Birefringence δ = 0.078
Optical character biaxial negative
Axis angle 2V = 85 ° (measured); 82 ° (calculated)
Pleochroism Visible:
X = light green
Y = light pink
Z = pink

Ahlfeldite is a very rarely occurring mineral from the mineral class of "oxides and hydroxides" (including V [5,6] vanadates, arsenites, antimonites, bismutites, sulfites, selenites, tellurites, iodates) with the idealized chemical composition Ni (SeO 3 ) · 2H 2 O and therefore, chemically speaking, a hydrous nickel - selenite .

Ahlfeldite crystallizes in the monoclinic crystal system , but rarely develops crystals up to about one millimeter in size that are visible to the naked eye with a glass-like sheen on the surfaces. So far it has mainly been found in the form of spherical mineral aggregates and crusty coatings of light, apple or olive green as well as brownish pink to brown in color. Ahlfeldit leaves a pale green to white line on the marking board .

With cobaltomenite (CoSeO 3 · 2H 2 O), ahlfeldite forms a mixed crystal row and the mixed formula can be given accordingly as (Ni, Co) [SeO 3 ] · 2H 2 O.

Etymology and history

According to the first description by Robert Herzenberg and Friedrich Ahlfeld , a rich silver ore vein was discovered in 1923 near the Hiaco lead-silver mine and about 30 km east-north-east of Colquechaca in the province of Chayanta in the Bolivian Department of Potosí , but this was due to the unfavorable ore distribution and the brittle side rock proved not to be degradable. The mineral samples collected from this vein by mining engineer Hans Block were analyzed by Herzberg and Ahlfeld in 1935. They were able to discover two previously unknown selenium minerals in it. The one with the chemical composition (Cu, Ni) Se 2 named Herzenberg in honor of its discoverer Blockit . For the other, which was found to be nickel seleniate through qualitative tests , Herzenberg suggested the name Ahlfeldite.

As type locality but Silbergrube applies Mina Virgen de Surumi (also Pacajake mine ) on the Hiaco opposite side of Pakajake Canyon , where the name Pacajake mine is to be a widespread misnomer. The well-known selenium minerals in this area have often been incorrectly attributed to either Hiaco or the Colquechaca mine , 28 km southwest .

The type material of ahlfeldite is in the Natural History Museum in London (England) under the catalog no. 1972,347 retained .

classification

Already in the outdated 8th edition of the mineral classification by Strunz of Ahlfeldit the mineral class of "oxides and hydroxides" and then to the Department of "Arsenites, Selenite, tellurites and iodates" where he and belonged Cobaltomenit and Molybdomenit the "Cobaltomenit series" with the system no. IV / G.02b .

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. IV / K.07-30 . In the “Lapis system” this corresponds to the section “Sulphites, Selenites, Tellurites” (with assemblies [XO 3 ] 2- and relatives), where ahlfeldite forms a common but unnamed group together with cobaltomenite , clinochalkomenite , millsite and nestolaite .

The 9th edition of Strunz's mineral systematics, valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also assigns ahlfeldite to the class of "oxides and hydroxides" and there to the department of "arsenites, antimonites, bismuthites, Sulfites, selenites, tellurites; Iodate ”. However, this is further subdivided according to, so that the mineral according to its composition in the sub-section “Selenite without additional anions; with H 2 O ”, where together with cobaltomenite and clinochalkomenite the“ cobaltomenite group ”with the system no. 4.JH.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the ahlfeldite to the class of "sulphates, chromates and molybdates" and there to the category of "selenites, tellurites and sulphites". Here it can be found in the unnamed group 02/34/03 within the subsection “ Selenites - Tellurites - Sulphites with A 2+ XO 3 × x (H 2 O) ”.

Chemism

The idealized, theoretical composition of ahlfeldite (Ni (SeO 3 ) 2H 2 O) consists of 58.69% nickel (Ni), 35.62% selenium (Se), 36.04% oxygen (O) and 1.82 % Hydrogen (H). Due to the mixed crystal formation with cobaltomenite, however, part of the nickel is usually replaced ( substituted ) by cobalt (Co ).

Crystal structure

Ahlfeldite crystallizes isotypically with cobaltomenite monoclinically in the space group P 2 1 / n (space group no. 14, position 2) with the lattice parameters a  = 7.52  Å ; b  = 8.75 Å; c  = 6.44 Å and β = 99.0 ° as well as four formula units per unit cell . Template: room group / 14.2

Education and Locations

Ahlfeldite forms as a secondary conversion product from nickel-containing selenides and sulphides. The accompanying minerals include angelsite , cerussite , chalcomenite , goethite , lepidocrocite , olsacherite and penrosite .

Apart from its type locality , the Mina Virgen de Surumi silver mine in the province of Chayanta, the mineral has so far only been discovered in the former "El Dragón" mine in the Antonio Quijarro province, which is also part of the Bolivian Department of Potosí ( Status 2019).

See also

literature

  • Robert Herzenberg, Friedrich Ahlfeld: Blockit, a new ore from Bolivia . In: Zentralblatt für Mineralogie, Geologie und Paläontologie . tape 6 , 1935, pp. 277–279 ( available online at rruff.info [PDF; 217 kB ; accessed on February 12, 2019]).
  • WF Foshag: New Mineral Names . In: American Mineralogist . tape 20 , 1935, pp. 678-678 (English, available online at rruff.info [PDF; 61 kB ; accessed on February 12, 2019]).
  • M. Wildner: Crystal structure refinements of synthetic cobaltomenite (CoSeO 3 · 2H 2 O) and ahlfeldite (NiSeO 3 · 2H 2 O) . In: New yearbook for mineralogy, monthly books . 1990, p. 353-362 (English).

Web links

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

Individual evidence

  1. ^ Paul Ramdohr: Two new minerals . In: Zentralblatt für Mineralogie, Geologie und Paläontologie. Abt. A . tape 6 , 1935, pp. 189-189 ( available online at rruff.info [PDF; 80 kB ; accessed on February 12, 2019]).
  2. ↑ a b c d e 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.  273 (English).
  3. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: September 2019. (PDF 2672 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, September 2019, accessed October 20, 2019 .
  4. ↑ a b c d Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  5. ^ David Barthelmy: Ahlfeldite Mineral Data. In: webmineral.com. Accessed February 11, 2019 .
  6. ↑ a b c d e f g h i Ahlfeldite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 68  kB ; accessed on February 11, 2019]).
  7. ↑ a b c d e f Ahlfeldite. In: mindat.org. Hudson Institute of Mineralogy, accessed February 11, 2019 .
  8. ↑ Robert Herzenberg, Friedrich Ahlfeld: Blockit, a new beer ore from Bolivia . In: Zentralblatt für Mineralogie, Geologie und Paläontologie . tape 6 , 1935, pp. 277–279 ( available online at rruff.info [PDF; 217 kB ; accessed on February 12, 2019]).
  9. ↑ Type locality Virgen de Surumi mine (Pacajake mine; Pakajake mine), Pakajake Canyon (Pacajake Canyon), Chayanta Province, Potosí, Bolivia. In: mindat.org. Hudson Institute of Mineralogy, accessed February 26, 2019 .
  10. ↑ Catalog of type mineral specimens - W. (PDF 59 kB) In: smmp.net. Commission on Museums (IMA), June 1, 2007, accessed February 5, 2019 .
  11. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 25, 2019 .
  12. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  561 (first edition: 1891).
  13. ↑ Find location list for ahlfeldite at the Mineralienatlas and at Mindat