Fiedlerite

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Fiedlerite
Fiedlerite-112692.jpg
Colorless fiedlerite crystals from the harbor slag locality, Lavrio, Attica, Greece (image width 3 mm)
General and classification
chemical formula Pb 3 (OH) FCl 4 • H 2 O
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.DC.10 ( 8th edition : III / D.08)
03/10/02/01
Crystallographic Data
Crystal system triclinic or monoclinic
Crystal class ; symbol triclinic pinacoidal 1 or monoclinic prismatic 2 / m
Space group see crystal structure
Lattice parameters see crystal structure
Formula units see crystal structure
Frequent crystal faces {100}, stretched according to [010]
Physical Properties
Mohs hardness ≈ 3.5
Density (g / cm 3 ) measured: 5.88; calculated: 5.15 (2M) or 5.69 (1A)
Cleavage good after {100}
colour colorless to white
Line color White
transparency transparent to translucent
shine Diamond luster
Crystal optics
Refractive indices n α  = 1.980
n β  = 2.040
n γ  = 2.100
Birefringence δ = 0.120
Optical character biaxial negative

Fiedlerite is a rarely occurring mineral from the mineral class of " halides " with the chemical composition Pb 3 (OH) FCl 4 · H 2 O, so it is a water-containing lead oxyhalide. From a crystallographic point of view, fiedlerite is a polytype , i.e. its crystal structure consists of a layer lattice with structural units crystallizing alternately in triclinic and monoclinic symmetry . To distinguish between these, they are sometimes referred to as fiedlerite-1A and fiedlerite-2M , but are not considered to be independent modifications and minerals.

Fiedlerit develops tabular, strip-shaped crystals and combinations up to about two millimeters in size with a diamond-like sheen on the surfaces. In their pure form, the crystals are colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline design , these can also appear white, with the transparency correspondingly decreasing.

Etymology and history

Fiedlerite was first discovered in the old slag heaps near Lavrio in the Greek region of Attica and described in 1887 by Gerhard vom Rath , who named the mineral after the Saxon commissioner for mining Karl Gustav Fiedler (1791-1853).

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the fiedlerite belonged to the mineral class of the "halides" and there to the department of the "oxyhalides", where together with laurionite it forms the "fiedlerite-laurionite group" with the system -No. III / D.08 and the other members challacolloite , cotunnite , hephaistosite , paralaurionite and pseudocotunnite .

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 fiedlerite to the “halides” class, but in the newly defined division of “oxyhalides, hydroxyhalides and related doubles” -Halides ". This is also further subdivided according to the metals occurring in the compound, so that the mineral can be found according to its composition in the subsection "With Pb (As, Sb, Bi) without Cu", where it is the only member of the unnamed group 3. DC.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns fiedlerite to the “halides” class and there to the “oxyhalides and hydroxyhalides”. Here he is to be found as the only member in the unnamed group 10.03.02 within the subdivision " Oxyhalides and hydroxyhalides with the formula A 3 (O, OH) 2 X q ".

Education and Locations

Fiedlerite with clear cracks from the Vrissaki slag locality, Lavrio, Attica, Greece (image width 3 mm)

Fiedlerite forms as a secondary reaction product from lead-containing slags with halogen-containing seawater . Depending on the location, cotunnite , laurionite , penfieldite and phosgenite can occur as accompanying minerals .

As a rare mineral formation, fiedlerite could only be detected at a few localities, whereby so far (as of 2014) a little more than 10 localities are known. At its type locality Lavrio in Greece, the mineral was found on several old slag heaps such as in the port of Laurion, at St. Nikolas, Mikrolimanou, Oxygon, Panormos, Passa Limani, Sounion, Thorikos, Tourkolimanon and Vrissaki.

The only known site in Germany so far is the Christian Levin colliery in Essen (North Rhine-Westphalia) and in Austria fiedlerite is only known from a slag dump near Waitschach in Carinthia.

Other previously known sites are Baratti in the Italian municipality of Piombino , Argent in the South African province of Gauteng and the slag locality "The Gannel Smelter" near Crantock near St Agnes in the English county of Cornwall.

Crystal structure

Fiedlerit-1A crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 8.57  Å ; b  = 8.04 Å; c  = 7.28 Å; α = 90.0 °; β = 102.0 ° and γ = 103.4 ° as well as two formula units per unit cell .

Fiedlerit-2M crystallizes monoclinically in the space group P 2 1 / a (space group no. 14) with the lattice parameters a  = 16.68  Å ; b  = 8.04 Å; c  = 7.28 Å and β = 102.6 ° as well as four formula units per unit cell .

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  176 .
  2. ↑ a b c Fiedlerite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 70.5 kB )
  3. ↑ a b Mindat - Fiedlerite
  4. ^ IMA / CNMNC List of Mineral Names; October 2103 (PDF 1.5 MB)
  5. ↑ Mindat - Number of localities for fiedlerite
  6. ↑ Find location list for fiedlerite in the Mineralienatlas and Mindat