Lukrahnite

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Lukrahnite
Lukrahnite-434429.jpg
Lukrahnite (yellow) from the type locality Tsumeb Mine near Tsumeb , Namibia (image width 0.5 mm)
General and classification
other names

IMA 1999-033

chemical formula CaCuFe 3+ (AsO 4 ) [(H 2 O) (OH)]
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana 		8.CG.20 ( 8th edition : VII / C.31)
02.33.02.03
Similar minerals Tsumcorite, Gartrellite, Zincgartrellite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 5.457  Å ; b  = 5.539 Å; c  = 7.399 Å,
α  = 68.43 °; β  = 68.90 °; γ  = 69.44 °
Formula units Z  = 1
Physical Properties
Mohs hardness 5, VHN 25  = 630 kg / mm 2
Density (g / cm 3 ) 4.18 (calculated)
Cleavage no
Break ; Tenacity not specified; brittle
colour yellow
Line color pale yellow
transparency transparent
shine matt on crystal surfaces, semi-diamond gloss on fractured surfaces
Crystal optics
Refractive indices n α  = 1.83
n β  = 1.834
n γ  = 1.89
Birefringence δ = 0.060
Optical character biaxial positive
Axis angle 2V = 30 °
Pleochroism moderate with X = yellow to Y = Z = pale yellow
Other properties
Chemical behavior only very slowly soluble in warm dilute hydrochloric acid

Lukrahnite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the triclinic crystal system with the chemical composition CaCuFe 3+ (AsO 4 ) [(H 2 O) (OH)] and is therefore chemically a water-containing calcium - copper - iron - zinc - arsenate with an additional hydroxide ion .

At its type locality, lukrahnite develops spherical aggregates with a maximum diameter of 0.5 mm, which are accompanied by beudantite , cuproadamine , konichalcite , wulfenite , quartz and chalcosine . The type locality of the mineral is the Tsumeb Mine near Tsumeb , Otjikoto Region , Namibia .

Etymology and history

A large number of "yellow coatings" from the "Tsumeb Mine" were also examined during an extensive survey of tsumcorite group minerals . Most of it turned out to be tsumcorite, gartrellite or zinc gartrellite - however, the diffractograms of two samples were noticeable. Although they resembled the diffractograms of zinc gartrellite or zinc-containing gartrellite, the d-values ​​indicated a smaller unit cell . Further analyzes showed that these samples were the calcium analogue of gartrellite and thus a new mineral phase. After additional investigations were carried out on this material, the new phase was presented to the International Mineralogical Association (IMA), which it recognized in 1999. In 2001 the mineral was described as Lukrahnite by a German-Austrian team of scientists led by Werner Krause , Günter Blass , Heinz-Jürgen Bernhardt and Herta Effenberger in the German science magazine "New Yearbook for Mineralogy, Monthly Books". The authors named the mineral after the German geologist and mineral collector Ludger Krahn (* 1957) from Krefeld , who handed over the first stage of this new mineral for investigation.

The type material for Lukrahnit is kept in the collection of the Institute for Mineralogy, Geology and Geophysics of the Ruhr University Bochum in Bochum , North Rhine-Westphalia .

classification

The current classification of the International Mineralogical Association (IMA) counts the lukrahnite to the tsumcorite group with the general formula Me (1) Me (2) 2 (XO 4 ) 2 (OH, H 2 O) 2 , in which Me (1), Me (2) and X different positions in the structure of the minerals of the tsumcorite group with Me (1) = Pb 2+ , Ca 2+ , Na + , K + and Bi 3+ ; Me (2) = Fe 3+ , Mn 3+ , Cu 2+ , Zn 2+ , Co 2+ , Ni 2+ , Mg 2+ and Al 3+ and X = As 5+ , P 5+ , V 5+ and represent S 6+ . To Tsumcoritgruppe include not only Lukrahnit still Cabalzarit , Cobaltlotharmeyerit , Cobalttsumcorit , Ferrilotharmeyerit , Gartrellit , Helmutwinklerit , Kaliochalcit , Krettnichit , Lotharmeyerit , Manganlotharmeyerit , Mawbyit , Mounanait , Natrochalcit , Nickellotharmeyerit , Nickelschneebergit , Nickeltsumcorit , Phosphogartrellit , Rappoldit , Schneebergit , Thometzekit , Tsumcorit , Yancowinnait and Zinc Gartrellite . Within the tsumcorite group, lukrahnite together with gartrellite, zinc gartrellite and phosphogartrellite form the "gartrellite subgroup" named after gartrellite.

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the lukrahnite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the division of "water-containing phosphates without foreign anions ", where it belongs together with cabalzarite, cobalt solder armyerite, cobalt sumcorite , Ferrilotharmeyerit, Gartrellite, Helmutwinklerit, Krettnichit, Lotharmeyerit, Manganlotharmeyerit, Mawbyit, Mounanait, Nickellotharmeyerit, Nickelschneebergit, Phosphogartrellite, Rappoldit, Schneebergit, Thometzekit, Tsumcorit and Gartrumellcorit-Group with the "Tsumcorit-Group". VII / C.31 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 lukrahnite 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 to the water of crystallization content , so that the mineral can be classified according to its composition in the subsection “With large and medium-sized cations; RO 4  : H 2 O = 1: 1 "is to be found, where together with the other members gartrellite, helmutwinklerite, phosphogartrellite, zinc gartrellite and rappoldite the" Helmutwinklerite group "with the system no. 8.CG.20 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns lukrahnite to the class of "phosphates, arsenates and vanadates" and there in the department of "composite phosphates, etc.". Here it is together with Gartrellite and Zinc Gartrellite in the " Gartrellite Group " with the system no. 43.02.02 within the sub-section " Compound phosphates etc., (anhydrous normally composed anions) ".

Chemism

Nine microprobe analyzes on lukrahnite from the Tsumeb mine showed mean values ​​of 11.42% CaO; 10.00% CuO; 8.19% ZnO; 0.69% PbO; 0.05 NiO; 0.15 CoO; 13.75% Fe 2 O 3 ; 0.37% Al 2 O 3 ; 47.72% As 2 O 3 , 0.16% P 2 O 5 , 0.09% SO 3 and 5.98% H 2 O (calculated) as well as lower (<0.05%) contents of Bi 2 O 3 and V 2 O 5 . On the basis of ten oxygen atoms , the empirical formula (Ca 0.98 Pb 0.02 ) Σ = 1.00 (Cu 0.60 Fe 0.83 Zn 0.48 Co 0.01 Al 0.04 ) was calculated from them Σ = 1.96 [(AsO 4 ) 1.99 (PO 4 ) 0.01 (SO 4 ) 0.01 ] Σ = 2.01 [(H 2 O) 1.22 (OH) 0.74 ] Σ = 1.96 . The simplified formula derived from this is Ca (Cu, Zn) (Fe, Zn) (AsO 4 ) 2 (H 2 O, OH) 2 , the zinc-free ideal formula CaCuFe 3+ (AsO 4 ) 2 [(H 2 O) (OH )].

As with gartrellite and zinc gartrellite, Cu and Fe 3+ occupy different crystallographic positions Me (2a) and Me (2b). Any Zn present occurs in equal parts at both positions, which leads to a variable hydroxide ion content according to [(H 2 O, OH) 2 ]. In the zinc-free lukrahnite end member, however, exactly one water molecule and one hydroxide ion according to [(OH) (H 2 O)] are present. Parts of the lukrahnite from the "Tsumeb Mine" are overgrown by a lead-containing lukrahnite variety with a Pb content of up to 7% by weight, which corresponds to a Ca-Pb ratio of 0.85: 0.15.

Lukrahnite is the Ca-dominant analogue of the Pb-dominated Gartrellite. In terms of chemical composition, lukrahnite is extremely similar to Ferrilotharmeyerite - apart from a partial substitution of Cu for Fe and Zn, which causes a change in the crystal symmetry, as the Tsumcorite group in the presence of significant amounts of both Cu and Fe 3+ splits the Me (2) position into two crystallographically different positions Me (2a) and Me (2b), which is due to the ordered arrangement of alternating CuO 6 - and Fe 3+ O 6 - polyhedron is conditional.

Crystal structure

Lukrahnite crystallizes in the triclinic crystal system in the space group P 1 (space group no. 2) with the lattice parameters a  = 5.457  Å ; b  = 5.539 Å; c  = 7.399 Å; αβ = 68.43; β = 68.90 ° and γβ = 69.44 ° and one formula unit per unit cell . Template: room group / 2

The mineral is isotypic (isostructural) to the triclinic representatives of the tsumcorite group such as gartrellite and zinc gartrellite.

properties

morphology

Lukrahnite develops spherical aggregates with a maximum diameter of 0.5 mm in the "Tsumeb Mine", whereby single crystals could not be observed. When crushing between two pieces of glass, however, almost single crystal-like fragments <30 µm in size are created. Tiny coatings <10 µm thick on a bismuth-containing nickellotharmeyerite from the “Pucherschacht” in Schneeberg, Saxony, turned out to be calcium-iron-copper arsenate according to microprobe analyzes, which is also assumed to be lukrahnite. Lukrahnite from the "Clara Pit" in the Black Forest consists of 0.2 mm large, hemispherical aggregates with a shell structure, whereby the spaces between the shells are partially hollow.

physical and chemical properties

The aggregates of Lukrahnite are yellow, their line color is pale or light yellow. The surfaces of the transparent aggregates are matt, while the fracture surfaces have a diamond-like sheen (semi -diamond sheen ). This diamond-like shine agrees well with the very high values ​​for light refraction (n α  = 1.830; n β  = 1.834; n γ  = 1.890) and the high value for birefringence (δ = 0.060) of Lukrahnite. Under the microscope , the mineral shows a moderate pleochroism from X = yellow to Y = Z = pale yellow in transmitted light .

Lukrahnite shows no cleavage , and no fracture is given for the brittle mineral . With a Mohs hardness of 5, the mineral is one of the medium-hard minerals and, like the reference mineral apatite , can be scratched with a pocket knife. The Vickers hardness VHN 25 was determined to be 630 kg / mm 2 . The calculated density for lukrahnite is 4.18 g / cm 3 . The mineral is neither in the long term nor in the short wavelength UV light , a fluorescent .

Lukrahnit is only slowly soluble in warm, dilute hydrochloric acid , HCl, without effervescence.

Education and Locations

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

Paragenesis minerals in the “Tsumeb Mine” are beudantite, cuproadamine, konichalcite, wulfenite, quartz and chalcosine. At the “Pucherschacht”, Lukrahnite is accompanied by Nickellotharmeyerite, while at the “Grube Clara” it appears with Konichalcite on quartz, as well as cuprite and solid copper .

As of 2018, Lukrahnite could only be described as a very rare mineral formation from four sites. The type locality is the "Tsumeb Mine" near Tsumeb, Otjikoto region, Namibia. The exact location for the mineral within the mine is unknown. The world's second location was Schneeberg in the Erzgebirge , Saxony , Germany . Lukrahnite was recovered from the pile material of the “Pucherschacht” in the “Wolfgang Maaßen” mine field. In Germany, Lukrahnite is also known from the Clara mine in the Rankach Valley near Oberwolfach , Black Forest , Baden-Württemberg . After all, lukrahnite is known from the Lavrion mining district , Attica region , Greece . However, there is no further information.

There are no known occurrences of lukrahnite in Austria or Switzerland .

use

Due to its rarity, lukrahnite is only of interest to mineral collectors.

See also

literature

  • Werner Krause, Günter Blaß, Heinz-Jürgen Bernhardt, Herta Effenberger: Lukrahnite, CaCuFe 3+ (AsO 4 ) 2 [(H 2 O) (OH)], the calcium analogue of gartrellite . In: New yearbook for mineralogy, monthly books . tape 2001 , no. 11 , 2001, p. 481-492 .

Web links

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

Individual evidence

  1. ↑ 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 ai aj ak al am an ao ap aq ar as at Werner Krause, Günter Blaß, Heinz-Jürgen Bernhardt, Herta Effenberger: Lukrahnite, CaCuFe 3+ (AsO 4 ) 2 [(H 2 O) (OH)], the calcium analogue of gartrellite . In: Neues Jahrbuch drove mineralogy, monthly books . tape 2001 , no. 11 , 2001, p. 481-492 .
  2. ↑ a b Lukrahnite. In: mindat.org. Hudson Institute of Mineralogy, accessed September 20, 2019 .
  3. ↑ Storage of the type level Lukrahnit. In: typmineral.uni-hamburg.de. University of Hamburg , accessed on September 20, 2019 .
  4. ↑ Catalog of Type Mineral Specimens - L. (PDF 70 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed September 20, 2019 .
  5. ↑ a b Werner Krause, Klaus Belendorff, Heinz-Jürgen Bernhardt, Catherine McCammon, Herta Effenberger, Werner Mikenda: Crystal chemistry of the tsumcorite-group minerals. New data on ferrilotharmeyerite, tsumcorite, thometzekite, mounanaite, helmutwinklerite, and a redefinition of gartrellite . In: European Journal of Mineralogy . tape 10 , no. 2 , 1998, p. 179–206 , doi : 10.1127 / ejm / 10/2/0179 (English).
  6. ↑ Herta Effenberger, Werner Krause, Heinz-Jürgen Bernhardt, Mirko Martin: On the symmetry of tsumcorite group minerals based on the new species rappoldite and zincgartrellite . In: Mineralogical Magazine . tape 64 , no. 6 , 2000, pp. 1109–1126 , doi : 10.1180 / 002646100549922 ( http://rruff.info/doclib/mm/vol64/MM64_1109.pdf rruff.info [PDF; 1.1 MB ; accessed on May 22, 2018]).
  7. ↑ a b Werner Krause, Herta Effenberger, Heinz-Jürgen Bernhardt, Mirko Martin: Cobalttsumcorite and nickellotharmeyerite, two new minerals from Schneeberg, Germany: description and crysral structure . In: Neues Jahrbuch drove mineralogy, monthly books . tape 2001 , no. 12 , 2001, p. 558-576 .
  8. ↑ a b c Uwe Kolitsch, Joachim Gröbner, Franz Brandstätter, Richard Bayerl: New finds from the Clara mine in the central Black Forest (IV) . In: Lapis . tape 35 , no. 9 , 2010, p. 22-27 .
  9. ↑ Localities for Lukrahnite. In: mindat.org. Hudson Institute of Mineralogy, accessed September 20, 2019 .
  10. ↑ a b List of localities for Lukrahnite at the Mineralienatlas and at Mindat (accessed on September 20, 2019)
  11. ↑ data sheet Lukrahnit. In: tsumeb.com. Retrieved September 20, 2019 .
  12. ↑ Uwe Kolitsch, Branko Rieck, Franz Brandstätter, Fritz Schreiber, Karl Heinz Fabritz, Günter Blaß, Joachim Gröbner: New discoveries from the old mining and slag from Lavrion (I) . In: Mineral World . tape 25 , no. 1 , 2014, p. 60-75 .