Crowning kit

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Crowning kit
Krohnkite-21581.jpg
Kröhnkit crystal specimen from the “ Chuquicamata Mine”, El Loa Province, Antofagasta, Chile (size: 6 cm × 4.3 cm × 3 cm).
General and classification
other names

Kroehnkit

chemical formula Na 2 Cu [SO 4 ] 2 • 2H 2 O
Mineral class
(and possibly department) 		Sulfates (including selenates, tellurates, chromates, molybdates, and tungstates)
System no. to Strunz
and to Dana 		7.CC.30 ( 8th edition : VI / C.16)
03/29/02/01
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  = 5.81  Å ; b  = 12.66 Å; c  = 5.52 Å
β  = 108.3 °
Formula units Z  = 2
Frequent crystal faces {110}, {011}, {010}, {021}, { 1 11}
Twinning after {101}
Physical Properties
Mohs hardness 2.5 to 3
Density (g / cm 3 ) measured: 2.90; calculated: 2.913
Cleavage completely after {010}, indistinct after { 1 01}
Break ; Tenacity shell-like
colour sky blue to light blue, greenish blue
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.544
n β  = 1.578
n γ  = 1.601
Birefringence δ = 0.057
Optical character biaxial negative
Axis angle 2V = measured: 78 °; calculated: 76 °
Other properties
Chemical behavior easily soluble in water

Kröhnkit (also Kroehnkit ) is a rarely occurring mineral from the mineral class of "sulfates (including selenates, tellurates, chromates, molybdates and wolframates)". It crystallizes in the monoclinic crystal system with the chemical composition Na 2 Cu [SO 4 ] 2 · 2H 2 O, so it is a water-containing sodium - copper - sulfate .

Kröhnkit usually develops short to long prismatic or pseudo octahedral crystals , but also occurs in the form of fibrous crusts and dense aggregates . The transparent to translucent crystals are sky-blue to light blue or greenish-blue in color and have a glass-like sheen . Kröhnkit leaves a white line on the marking board .

With a Mohs hardness of 2.5 to 3, Kröhnkit is one of the soft to medium-hard minerals that, like the reference mineral calcite, can be easily scratched with a copper coin.

Etymology and history

The mineral was first discovered in an open-cast copper mine near Chuquicamata (Chuquicamata Mine) in the Chilean Atacama Desert, which was sold from there as copper vitriol . However, the chemist and then German consul in Chile Berthold Kröhnke noticed the unusually light, blue color of the crystals. He therefore took some crystals with him, analyzed them and passed on his analysis results and some descriptions of the mineral in a letter to Ignacy Domeyko in 1875 . He was able to confirm the results of the investigation by Kröhnke and named the new mineral after the person who first described it, although he alternated between Krönke and Kronnke .

Ludwig Darapsky corrected the mineral name in 1889 in his summary of the correspondence in Kröhnkit , as he considered this spelling to be the correct one.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the Kröhnkit belonged to the mineral class of "sulfates (selenates, tellurates, chromates, molybdates and wolframates)" and there to the department of "water-containing sulfates, without foreign anions ", where together with Goldichit he created the "Kröhnkit-Goldichit-Gruppe" with the system no. VI / C.16 and the other member Ferrinatrite 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 Kröhnkit to the category of "Sulphates (selenates, etc.) without additional anions, with H 2 O". However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With medium-sized and large cations”, where it is the only member of the unnamed group 7.CC.30 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Kröhnkit to the class of "sulfates, chromates and molybdates" and there to the category of "water-containing acids and sulfates". Here he is to be found as the only member of the unnamed group 29.03.02 within the sub-section “ Hydrous acids and sulfates with (A + ) 2 B (XO 4 ) 2 × x (H 2 O) ”.

Crystal structure

Kröhnkit crystallizes monoclinically in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 5.81  Å ; b  = 12.66 Å; c  = 5.52 Å and β = 108.3 ° and two formula units per unit cell . Template: room group / 14

The crystal structure of Kröhnkit consists of corner-sharing CuO 4 (H 2 O) - octahedra and SO 4 - tetrahedra which are parallel to [001] lined up to form chains. These chains are connected by Na [7] polyhedra and hydrogen bonds.

properties

Kröhnkit crackles in front of the soldering tube and melts into a green mass that shatters after cooling. The mineral is easily soluble in water and the solution is acidic.

Education and Locations

Handpiece made of blue crown kit with greenish natrochalcite as a crack filling from the Chuquicamata Mine, Chile (size: 9.2 cm × 5.0 cm × 4.7 cm).

Kröhnkit forms secondarily in the oxidation zone of copper deposits , preferably under very dry climatic conditions. As accompanying minerals may include Antlerit , Atacamit , bloedite , Chalkanthit and Natrochalcit occur.

As a rare mineral formation, Kröhnkit could only be detected at a few sites, with around 20 sites being known to date (as of 2014). In addition to its type locality "Chuquicamata Mine", the mineral appeared in Chile in other pits in the area around Chuquicamata and Calama as well as at Mejillones and in several pits near Caracoles .

The only known site in Austria so far is a slag dump near Walchen (municipality of Öblarn ) in Styria.

Other locations include Argentina, Australia, China, Greece, Italy, Romania, Hungary, England in the United Kingdom (UK) and California and Virginia in the United States of America (USA).

See also

literature

  • Ignacy Domeyko: Crown kit. In: Mineralojía Libreria Central de Servat I CA. Santiago, Chile, pp. 250-252 ( rruff.info PDF 438.8 kB).
  • L. Darapsky: Communications to the editors. About crown kit. In: M. Bauer, W. Dames, Th. Liebisch (Hrsg.): New year book for mineralogy, geology and palaeontology. Volume IE Schweizbart'sche Verlagshandlung, Stuttgart 1889, pp. 192–195 ( Textarchiv - Internet Archive ).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 610 (first edition: 1891).
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 680 .

Web links

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

Individual evidence

  1. ↑ a b c d 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.  389 .
  2. ↑ a b c Kröhnkite. 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 65.9 kB).
  3. ↑ a b c d e Mindat - Kröhnkite
  4. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  5. ↑ Sir Humphry Davy, et al .: Metall und Erz. 1913, p. 142. Excerpt from Google Books
  6. ^ L. Darapsky: Communications to the editors. About crown kit. in: M. Bauer, W. Dames, Th. Liebisch (Hrsg.): New yearbook for mineralogy, geology and palaeontology. Volume IE Schweizbart'sche Verlagshandlung, Stuttgart 1889, p. 192 ( Textarchiv - Internet Archive ).
  7. ^ L. Darapsky: Communications to the editors. About crown kit. in: M. Bauer, W. Dames, Th. Liebisch (Hrsg.): New yearbook for mineralogy, geology and palaeontology. Volume IE Schweizbart'sche Verlagshandlung, Stuttgart 1889, p. 193 ( Textarchiv - Internet Archive ).
  8. ^ L. Darapsky: Communications to the editors. About crown kit. In: M. Bauer, W. Dames, Th. Liebisch (Hrsg.): New year book for mineralogy, geology and palaeontology. Volume IE Schweizbart'sche Verlagshandlung, Stuttgart 1889, p. 195 ( Textarchiv - Internet Archive ).
  9. ↑ Mindat - Number of localities for Kröhnkite
  10. ↑ Find location list for Kröhnkit at the Mineralienatlas and at Mindat