Paulkellerit

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Paulkellerit
General and classification
other names

IMA 1987-031

chemical formula Bi 2 Fe 3+ (PO 4 ) O 2 (OH) 2
Mineral class
(and possibly department)
Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana
8.BM.10 ( 8th edition : VII / B.37)
03.41.08.01
Similar minerals Brendelite , Kolitschite , Neustädtelite , Medenbachite , Retzian
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic, 2 / m
Room group (no.) C 2 / c (No. 15)
Lattice parameters a  = 11.38  Å ; b  = 6.66 Å; c  = 9.65 Å
β  = 115.3 °
Formula units Z  = 4
Frequent crystal faces dominant: {110} and {011};
weakly pronounced: { 1 01}
Physical Properties
Mohs hardness 4th
Density (g / cm 3 ) > 4.2 (measured); 6.17 (calculated)
Cleavage no
colour greenish yellow
Line color pale yellow
transparency transparent
shine Glass to diamond gloss
Crystal optics
Refractive indices n α  = 1.762
n β  = 1.767
n γ  = 1.825
Birefringence δ = 0.063
Optical character biaxial positive
Axis angle 2V = 34 ° (calculated); 37 ° (measured)
Pleochroism absent / imperceptible

Paulkellerite is a rarely occurring mineral from the mineral class of phosphates , arsenates and vanadates . It crystallizes in the monoclinic crystal system with the chemical composition Bi 2 Fe (PO 4 ) O 2 (OH) 2 and develops prismatic single crystals with a size in the sub-millimeter range and a greenish-yellow color.

Etymology and history

The mineral was named after Paul Keller (* 1940), professor of mineralogy at the University of Stuttgart .

Paulkellerit was purified on a dating from the 1881 sample of the Saxon bismuth , nickel and cobalt-containing ore - deposits in the collection of Freiberg discovered. The sample was from the NW - SE - trending vein Neuhilfe flat in the pit Young calving at Neustädtel ( Snow Mountain , Ore removed). This site is also considered a type locality .

Until it was first described in 1988 by Pete J. Dunn , Joel D. Grice , Frederick J. Wicks and Richard A. Gault , the Paulkellerite contained therein was incorrectly identified as chemical due to its similar color and the same crystal class (monoclinic prismatic, 2 / m ) related arsenate atelestite Bi 8 (AsO 4 ) 3 O 5 (OH) 5 held. With the help of chemical analyzes, however, it was possible to prove beyond doubt that the mineral is a phosphate and not an arsenate, and iron was also detected as a component of the mineral. From the chemical analysis an empirical formula according to Bi 2 Fe (PO 4 ) O 2 (OH) 2 could be established, which is in very good agreement with the ideal formula Bi 2 Fe (PO 4 ) O 2 (OH) determined from crystal structure analyzes. 2 stands.

The holotype of the specimen from the first description is now held by the Smithsonian Institution under number NMNH 163777 . Further samples of the material are in the Canadian Museum of Nature in Ottawa ( NMNS 53450 ) and at the Bergakademie Freiberg .

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , the Paulkellerite belongs to the department of "Anhydrous phosphates with foreign anions ". The new Strunz'sche mineral classification now subdivides here more precisely according to the size of the cations involved and the molar ratio of the anions involved and the phosphate, arsenate or vanadate complex. The mineral is now in the sub-section "With medium-sized and large cations (OH, etc.): RO 4 = 4: 1".

The systematics of minerals according to Dana , which is common in the English-speaking world , also assigns Paulkellerite to the class of phosphates, arsenates and vanadates and there in the division of " anhydrous phosphates etc., with hydroxyl or halogen and the general formula (AB) 3 (XO 4 ) Z q “, where he and Brendelit form the unnamed group 41.03.08 .

Education and Locations

Paulkellerite occurs as a secondary mineral in bismuth-nickel-copper ore deposits in paragenesis with native bismuth, skutterudite , pyrite , erythrin , bismuth ferrite .

So far, the mineral could only be detected at its type locality.

morphology

Crystal form of Paulkellerite

The wedge-shaped crystals of Paulkellerit reach a size of 0.2 to 0.8 mm. Since Paulkellerite is a secondary mineral , the crystals can grow largely undisturbed on rock surfaces or other minerals and are therefore mostly idiomorphic . The very simple crystal morphology is mainly made up of slightly curved prismatic surfaces {110} and {011}, in addition there is a weakly developed pinacoid { 1 01}. The ideal crystal form of Paulkellerite is shown in the figure on the right.

Crystal structure

Paulkellerite crystallizes monoclinically in the space group C 2 / c with the lattice parameters a  = 11.38  Å , b  = 6.66 Å, c  = 9.65 Å and β  = 115.3 ° as well as four formula units per unit cell .

See also

Individual evidence

  1. a b c J. D. Grice, LA Groat: The crystal structure of paulkellerite . In: American Mineralogist , Vol. 73, 1988, pp. 873-875.
  2. JD Grice, LA Groat: The crystal structure of paulkellerite . In: American Mineralogist , Vol. 73, 1988, pp. 873-875.

literature

  • PJ Dunn, JD Grice, FJ Wicks, RA Gault: Paulkellerite, a new bismuth iron phosphate mineral from Schneeberg, Germany In: American Mineralogist , Vol. 73, 1988, pp. 870-872.
  • JD Grice, LA Groat: The crystal structure of paulkellerite . In: American Mineralogist , Vol. 73, 1988, pp. 873-875.

Web links

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