Coskrenite (Ce)

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Coskrenite (Ce)
Coskrenite- (Ce) .jpg
Tabular pink coskrenite (Ce) crystals approx. 0.8 mm in size on apjohnite containing magnesium from Alum Cave Bluff , Great Smoky Mountains , Tennessee, USA
General and classification
other names

IMA 1996-056

chemical formula (Ce, Nd, La) 2 (SO 4 ) 2 (C 2 O 4 ) • 8H 2 O
Mineral class
(and possibly department) 		Organic compounds
System no. to Strunz
and to Dana 		10.AB.65 ( 8th edition : IX / A.01)
50.01.09.02
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 6.007  Å ; b  = 8.368 Å; c  = 9.189 Å,
α  = 99.90 °; β  = 103.55 °; γ  = 107.71 °
Formula units Z  = 1
Frequent crystal faces {100}, {010}, {001}
Physical Properties
Mohs hardness not definable
Density (g / cm 3 ) 2,881 (calculated)
Cleavage very perfect after {001}
Break ; Tenacity brittle; not specified
colour pale pink (incandescent light) to creamy white, pale blue (fluorescent light), colorless (sunlight)
Line color colorless (i.e. white)
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.544
n β  = 1.578
n γ  = 1.602
Birefringence δ = 0.058
Optical character biaxial negative
Axis angle 2V = 65 ° (measured), 69 ° (calculated)
Other properties
Chemical behavior easily soluble in water
Special features alexandrite-like color change in different types of light

Coskrenit- (Ce) is a very rarely occurring mineral from the mineral class of " organic compounds ". It crystallizes in the triclinic crystal system with the chemical formula (Ce, Nd, La) 2 (SO 4 ) 2 (C 2 O 4 ) · 8H 2 O, and is thus chemically seen a crystal water-containing cerium - sulphate - oxalate .

Coskrenite- (Ce) of the type locality forms aggregates of idiomorphic, tabular-wedge-shaped crystals with diamond-shaped cross-section, which are embedded in epsomite or apjohnite or sit in cavities in these minerals.

The mineral comes from "Alum Cave Bluff", a popular tourist attraction in Great Smoky Mountains National Park, Tennessee, where it is formed from the weathering of a pyrite-containing phyllite . The name can be translated as "Alaunhöhlenteilklippe", but there is no cave here, only the above-mentioned, approx. 30 m high cliff, which forms a 10 m deep overhang, in whose protection the water-soluble oxalate minerals are preserved.

Etymology and history

In 1981 T. Dennis Coskren from Columbia , Maryland began investigating an unusual mineralization at the "Alum Cave Bluff". These investigations led to the identification of a large number of unusual minerals typical of an evaporation environment. However, some phases could not be characterized initially and were given to the Mineralogical Laboratory at the University of Michigan for identification, where it was found that three of these phases are rare metal and sulfate-containing oxalates. Only after further extensive investigations were the data required by the International Mineralogical Association (IMA) completed, so that the first of these minerals was recognized by the IMA in 1996 under the number IMA 1996-056. In 1999 it was described by a US research team with Donald R. Peacor , Roland C. Rouse and Eric J. Essene in the Canadian science magazine "The Canadian Mineralogist" as Coskrenit- (Ce).

The mineral was named after the American geochemist and geologist T. Dennis Coskren (* 1942), who has been working on the mineralization of "Alum Cave Bluff" in detail since 1981. The Levinson Modifier [the suffix "- (Ce)"] indicates the dominant rare earth metal (here: Cer), as the IMA guidelines require when naming minerals containing rare metals .

The type of material for Coskrenit- (Ce) is at the University of Michigan , Ann Arbor / Michigan , and the Smithsonian Institution belonging to National Museum of Natural History , Washington, DC , kept.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Coskrenit- (Ce) belonged to the mineral class of "organic compounds" and there to the department of "salts of organic acids", where together with Caoxit , Glushinskit , Humboldtin , Levinsonite (Y) , lindbergite , minguzzite , moolooite , natroxalate , novgorodovaite , oxammite , stepanovite , Weddellite , wheatleyite , whewellite , zhemchuzhnikovite and Zugshunstit- (Ce) the independent "group of oxalates " with the system no. IX / A.01 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 Coskrenit- (Ce) to the class of "organic compounds" and there to the department of "salts of organic acids" a. However, this section is further subdivided according to the type of salt-forming acid , so that the mineral can be found according to its composition in the sub-section "Oxalates", where it is the only member of the unnamed group 10.AB.65 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Coskrenit- (Ce) to the class of "organic minerals" and there in the department of the same name. Here it is with Zugshunstit- (Ce) and Levinsonit- (Y) in the "Zugshunstitgruppe" with the system no. 50.01.09 within the sub-section “ Salts of organic acids (oxalates) ”.

Chemism

Mean values ​​from microprobe analyzes on Coskrenit- (Ce) from the “Alum Cave Bluff” led to contents of 0.1% Y 2 O 3 , 4.6% La 2 O 3 , 25.9% Ce 2 O 3 , 2.1 % Pr 2 O 3 , 13.3% Nd 2 O 3 , 1.0% Sm 2 O 3 , 0.8% Eu 2 O 3 , 0.3% Gd 2 O 3 , 22.6% SO 3 , 0 , 3% F, [10.2%] C 2 O 3 and [20.4%] H 2 O (the last two calculated from stoichiometry). This resulted in the empirical formula (Ce 1.06 Nd 0.56 La 0.20 Pr 0.09 Sm 0.04 Eu 0.03 Gd 0.01 Y 0.01 ) Σ = 2.00 (SO 4 ) 2 (C 2 O 4 ) 8H 2 O, simplified to (Ce, Nd, La) 2 (SO 4 ) 2 (C 2 O 4 ) 8H 2 O

Crystal structure

Coskrenit- (Ce) crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 6.007  Å ; b  = 8.368 Å; c  = 9.189 Å; α = 99.90 °; β = 103.55 ° and γ = 107.71 ° and one formula unit per unit cell . Template: room group / 2

In the structure of Coskrenit- (Ce) are four rings of two SEE (O, H 2 O) - polyhedra and two SO 4 - tetrahedra through common oxygen atoms connected to the oxalate groups to form chains parallel to [110]. Adjacent chains are linked by the oxalate groups to form layers parallel [001]. The layers are only weakly connected to one another by hydrogen bonds .

properties

morphology

Coskrenit- (Ce) typically forms wedge-shaped crystals up to 0.8 mm in size. They are flat-paneled according to the first pinacoid {100}, which represents the supporting crystal shape, and are delimited by the second pinacoid {010} and the third pinacoid {001} in such a way that diamond-shaped cross-sections result. The crystals often come together to form radially aggregated structures.

physical and chemical properties

Because of the cerium content, coskrenite (Ce) crystals show alexandrite-like color effects with a pale blue-gray color in the fluorescent light of fluorescent tubes and white color in the light of an incandescent lamp. They are colorless in sunlight. The crystals rarely show a creamy white color. Their line color is indicated as colorless. Since the line color corresponds to the powder color and the mineral powder cannot be colorless, the color of the line should best be described as white. The surfaces of the transparent crystals show a clear glass-like sheen .

The mineral shows very perfect cleavage according to {001}, but breaks very easily due to its brittleness. Because of the small crystal size, neither its Mohs hardness nor Vickers hardness could be determined. Measured values ​​for the density of Coskrenit- (Ce) do not exist, the calculated density for the mineral is 2.881 g / cm³.

Coskrenit- (Ce) is easily soluble in water without leaving any residue.

Education and Locations

As a very rare mineral formation, Coskrenit- (Ce) could only be described from one source so far (as of 2016). Its type locality is the rocky cliff of the "Alum Cave Bluff" in the Great Smoky Mountains National Park , Sevier County , Tennessee , United States . Accompanying minerals are magnesium-containing apjohnite and epsomite and sometimes also slavikite , ammoniojarosite , Tschermigite , levinsonite (Y) and / or Zugshunstite (Ce).

Coskrenit- (Ce) is a typical secondary formation that occurs in the soils of the “Alum Cave Bluff”. The name of the location is misleading as it is not a cave but a steep, overhanging rock cliff. The cliff and the surrounding rock form part of the Precambrian Anakeesta Formation, a metapelite with the texture of a phyllite, the main minerals of which are muscovite , biotite , chlorite , quartz and pyrite. This area is extremely rainy with rainfall of 2000 mm per year. The resulting weathering of the rock on the cliff also includes the oxidation of the pyrite and the dissolution of the main rock-forming silicates . This, in turn, leads to sulfate-rich solutions with low pH values that are rich in elements from the dissolved silicates such as iron , magnesium , aluminum , potassium , sodium , calcium and manganese . When these solutions drip down the walls of the cliff, they get under the sloping surface of the rock overhang, where partial evaporation leads to the precipitation of sulphates, especially those of iron. Most of the water then continues to the bottom at the base of the cliff, where complete evaporation causes the creation of a wide variety of minerals, mainly hydrated and / or hydrated sulfates. These precipitates consist mainly of epsomite and members of the hair salt family, among which apjohnite is the most common mineral.

use

Coskrenit- (Ce) is only of interest to mineral collectors due to its rarity.

See also

literature

  • Coskrenite- (Ce) . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 69 kB ; accessed on March 10, 2019]).
  • Donald R. Peacor, Roland C. Rouse, Eric J. Essene: Coskrenite- (Ce), (Ce, Nd, La) 2 (SO 4 ) 2 (C 2 O 4 ) .8H 2 O, a new rare-earth oxalate mineral from Alum Cave Bluff, Tennessee: Characterization and crystal structure . In: The Canadian Mineralogist . tape 37 , 1999, pp. 1453–1462 (English, available online at rruff.info [PDF; 1.1 MB ; accessed on March 11, 2019]).

Web links

Commons : Coskrenite- (Ce)  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o Donald R. Peacor, Roland C. Rouse, Eric J. Essene: Coskrenite- (Ce), (Ce, Nd, La) 2 (SO 4 ) 2 (C 2 O 4 ) 8H 2 O, a new rare-earth oxalate mineral from Alum Cave Bluff, Tennessee: Characterization and crystal structure . In: The Canadian Mineralogist . tape 37 , 1999, pp. 1453–1462 ( rruff.info [PDF; 1.1 MB ; accessed on March 11, 2019]).
  2. ^ A b c T. Dennis Coskren, Robert J. Lauf: The Minerals of Alum Cave Bluff, Great Smoky Mountains, Tennessee . In: The Mineralogical Record 2000 . tape 31 , 2000, pp. 163-175 .
  3. ^ Coskrenite- (Ce) . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 69  kB ; accessed on March 11, 2019]).
  4. ↑ Catalog of Type Mineral Specimens - C. (PDF 130 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed June 29, 2019 .
  5. ^ 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.  720-721 .
  6. ↑ Localities for Coskrenite- (Ce). In: mindat.org. Hudson Institute of Mineralogy, accessed March 11, 2019 .
  7. ↑ Find location list for Coskrenit- (Ce) at the Mineralienatlas and at Mindat
  8. ^ Robert J. Lauf: Secondary Sulfate Minerals From Alum Cave Bluff: Microscopy and Microanalysis . 1st edition. Oak Ridge National Laboratory, Oak Ridge, Tennessee 1997, p. 1–43 , doi : 10.2172 / 631175 ( available online at digital.library.unt.edu [PDF; 10.7 MB ; accessed on March 11, 2019]).