Table dorfite

Table dorfite
	Incident light image with table villageite (tsh), Chrisstanleyite (c), Clausthalite (cla), Tiemannite (tie) and some stibiopalladinite in a matrix of black anchorite from the Eskaborner tunnel, Tilkerode (Abberode), Saxony-Anhalt (field of view: 275 μm)
General and classification
other names	IMA 2001-061
chemical formula	Pd 8 Hg 3 Se 9
Mineral class; (and possibly department)	Sulfides and sulfosalts
System no. to Strunz ; and to Dana	2.BC.65 ( 8th edition : II / A.06) ; 07/02/06/01
Similar minerals	Vasilite, Oosterboschit, Luberoite, Chrisstanleyite
Crystallographic Data
Crystal system	orthorhombic
Crystal class ; symbol	orthorhombic-dipyramidal; 2 / m 2 / m 2 / m or orthorhombic-pyramidal; mm 2
Space group	Pmmn (No. 59) or Pmn 2 1 (No. 31)
Lattice parameters	a = 7.219 Å ; b = 16.782 Å; c = 6.467 Å
Formula units	Z = 2
Twinning	no
Physical Properties
Mohs hardness	not specified
Density (g / cm 3 )	9.13 (calculated)
Cleavage	not specified
Break ; Tenacity	uneven; brittle
colour	not definable
Line color	black
transparency	opaque (opaque)
shine	Metallic luster

Tischendorfite is a very rarely occurring mineral from the mineral class of " sulfides and sulfosalts " with the idealized chemical formula Pd ₈ Hg ₃ Se ₉ . From a chemical point of view, table dorfite is therefore a palladium - mercury - selenide , which is structurally related to sulfides.

Tischendorfite crystallizes in the orthorhombic crystal system and develops exclusively xenomorphic to subidiomorphic aggregates as well as isolated subidiomorphic crystals up to a few hundred micrometers in size. Well-formed crystals are unknown.

Etymology and history

Already in 1958, the mineralogist and geochemist Gerhard Tischendorf had identified two potentially new minerals while examining selenides from the Eskaborner tunnel near Tilkerode in the Harz Mountains, but these could not be further determined due to the limited methods at the time. It was not until the beginning of the 1990s that both phases were examined using electron beam microanalysis and recognized as two new minerals with the chemical composition Ag ₂ Pd ₃ Se ₄ and Pd ₈ Hg ₃ Se ₉ . While Ag ₂ Pd ₃ Se _{4 was} finally first described by Hope's Nose , Torquay , Devon (England) , the second mineral was discovered in 2002 by an international research team with Chris J. Stanley, Alan J. Criddle, Hans-Jürgen Förster and Andrew C. Roberts from the Eskaborner tunnel can be described as table villageite.

The mineral was recognized by the International Mineralogical Association (IMA) in 2001 and named after its discoverer, the mineralogist and geochemist Gerhard Tischendorf (1927–2007).

Type material of the mineral is in the Natural History Museum , London , (catalog no. BM 2003,4) (holotype), in the Mineralogical Institute of the Technical University Bergakademie Freiberg in Germany (no. 80160) (Cotyp), in the GeoForschungsZentrum Potsdam as well as in the Systematic Reference Series of the National Mineral Collection of Canada, Geological Survey of Canada in Ottawa .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the table villageite belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "alloys and alloy-like compounds", where together with Chrisstanleyite , Jagüéit , Luberoit , Oosterboschit and Vasilit is an independent group with the system no. II / A.06 .

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 table dorfite to the class of "sulfides and sulfosalts" and there in the department of "metal sulfides, M: S> 1: 1 (mainly 2: 1) ”. This is, however, further subdivided according to the predominant metals in the compound, so that the mineral, according to its composition, can be found in the sub-section "with rhodium (Rh), palladium (Pd), platinum (Pt) etc.", where it is the only one Member forms the unnamed group 2.BC.65 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns table dorfit to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here he is the only member of the unnamed group 07/02/06 within the subsection “Sulphides - including selenides and tellurides - with the composition A _m B _n X _p , with (m + n): p = 9: 8”.

Crystal structure

Tischendorfite crystallizes in the orthorhombic crystal system in the space group Pmmn (space group no. 59) or space group Pmn 2 ₁ (space group no. 31) with the lattice parameters a = 7.219 Å ; b = 16.782 Å; c = 6.467 Å and β = 100.07 °; as well as two formula units per unit cell . Template: room group / 59 Template: room group / 31

There are three independent Pd, two independent Hg and four independent Se positions in the crystal structure of table dorfite. Tischendorfite crystallizes in a framework structure in which Pd atoms have two types of coordination by Se atoms: planar [PdSe ₄ ] squares and [PdSe ₅ ] pyramids. The [PdSe ₅ ] pyramid has two opposite Se-Se edges with neighboring pyramids and forms linearly isolated chains along the a-axis, while the [PdSe ₄ ] squares form pairs over a common Se-Se edge. The square pairs and chains of pyramids form characteristic plates parallel to (010). Both plate types alternate in the direction of the b-axis [010]. The Hg atoms occupy the anti-cubooctahedral cavities formed by Se atoms. The crystal structure is stabilized by a system of Pd-Hg and Pd-Pd metal bonds.

properties

morphology

Tischendorfite is never found in clear crystals, but exclusively in the form of xenomorphic to subidiomorphic grains up to a hundred micrometers in size, which form adhesions with other selenides in aggregates up to several hundred micrometers in size. The type level selenides dominated by Tiemannite show a cluster-like formation, which indicates a possible formation from a gel.

physical and chemical properties

The color of the aggregates of the table dorfite in the handpiece cannot be determined due to the small size of the aggregates. The line color of the opaque, shiny metal table villageite is described as black. Tischendorfite is brittle and has an uneven break. The calculated density of the mineral is 9.13 g / cm ³ .

In the reflected light (bevel), Tischendorfit is cream to light beige in color, shows weak bireflectance, no pleochroism and no internal reflections. With crossed polars the mineral shows a weak anisotropy with weak to moderate rotational colors in shades from steel blue to greenish brown. There is only a slight increase in the rotational colors in oil.

Education and Locations

Tischendorfite is found in hydrothermal , low-temperature, selenium-rich ore veins . It is associated with tiemannite , clausthalite , christianleyite , stibiopalladinite and gold in a matrix of calcite and anchorite .

So far (as of 2016) the mineral could only be detected at its type locality, the "Eskaborner tunnel" (60 m level, 5 m north of Blind Shaft IV) near Tilkerode , Harz , Saxony-Anhalt , Germany .

use

Table villageite with the end link composition Pd ₈ Hg ₃ Se ₉ consists of about 39% palladium, about 28% mercury and about 33% selenium. However, due to its rarity, table villageite is technically completely insignificant as a raw material for these elements.

literature

Chris J. Stanley, Alan J. Criddle, Hans-Jürgen Förster, Andrew C. Roberts: Tischendorfite, ideally Pd ₈ Hg ₃ Se ₉ , a new mineral species from Tilkerode, Harz Mountains, Germany . In: The Canadian Mineralogist . tape 40 , no. 2 , 2002, p. 739–745 , doi : 10.2113 / gscanmin.40.2.739 (English, rruff.info [PDF; 180 kB ; accessed on June 9, 2020]).
Table dorfite . 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; 95 kB ; accessed on June 15, 2020]).

Web links

Mineral Atlas: Tischendorfite (Wiki)
Table dorfite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 15, 2020 .
David Barthelmy: Tischendorfite Mineral Data. In: webmineral.com. Retrieved June 15, 2020 .
American-Mineralogist-Crystal-Structure-Database - Tischendorfite. In: rruff.geo.arizona.edu. Retrieved June 15, 2020 .

Individual evidence

^ Bernhard Pracejus: The ore minerals under the microscope, An optical guide . 2nd Edition. Elsevier, Amsterdam 2015, ISBN 978-0-444-62725-4 , pp. 180-181 (English).
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o Chris J. Stanley, Alan J. Criddle, Hans-Jürgen Förster, Andrew C. Roberts: Tischendorfite, ideally Pd ₈ Hg ₃ Se ₉ , a new mineral species from Tilkerode, Harz Mountains, Germany . In: The Canadian Mineralogist . tape 40 , no. 2 , 2002, p. 739–745 , doi : 10.2113 / gscanmin.40.2.739 (English, rruff.info [PDF; 180 kB ; accessed on June 9, 2020]).
↑ František Laufek, Anna Vymazalová, Milan Drábek, Jiří Navrátil, Jan Drahokoupil: Synthesis and crystal structure of tischendorfite, Pd ₈ Hg ₃ Se ₉ . In: The Canadian Mineralogist . tape 26 , no. 1 , 2014, p. 157–162 , doi : 10.1127 / 0935-1221 / 2013 / 0025-2345 (English).

[Pracejus-1] Bernhard Pracejus: The ore minerals under the microscope, An optical guide . 2nd Edition. Elsevier, Amsterdam 2015, ISBN 978-0-444-62725-4 , pp. 180-181 (English).

[Stanley-2] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o Chris J. Stanley, Alan J. Criddle, Hans-Jürgen Förster, Andrew C. Roberts: Tischendorfite, ideally Pd ₈ Hg ₃ Se ₉ , a new mineral species from Tilkerode, Harz Mountains, Germany . In: The Canadian Mineralogist . tape 40 , no. 2 , 2002, p. 739–745 , doi : 10.2113 / gscanmin.40.2.739 (English, rruff.info [PDF; 180 kB ; accessed on June 9, 2020]).

[Laufek_et_al_2014-3] František Laufek, Anna Vymazalová, Milan Drábek, Jiří Navrátil, Jan Drahokoupil: Synthesis and crystal structure of tischendorfite, Pd ₈ Hg ₃ Se ₉ . In: The Canadian Mineralogist . tape 26 , no. 1 , 2014, p. 157–162 , doi : 10.1127 / 0935-1221 / 2013 / 0025-2345 (English).