Earlandite

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Earlandite
General and classification
chemical formula
  • Ca 3 (C 6 H 5 O 7 ) 2 4H 2 O (empirical formula)
  • Ca 3 [CH 2 (COO) -CHOH (COO) -CH 2 (COO)] 2 · 4H 2 O (structural formula)
Mineral class
(and possibly department) 		Organic compounds
System no. to Strunz
and to Dana 		10.AC.10 ( 8th edition : IX / A.02)
02.50.02.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol Please complete!
Lattice parameters a  = 30.94  Å ; b  = 5.93 Å; c  = 10.56 Å
β  = 93.7 °
Formula units Z  = 4
Physical Properties
Mohs hardness Please complete!
Density (g / cm 3 ) measured: 1.80 to 1.95; calculated: 1.96
Cleavage Please complete!
colour white, pale yellow
Line color White
transparency translucent
shine Please complete!
Crystal optics
Refractive indices n α  = 1.515
n β  = 1.530
n γ  = 1.580
Birefringence δ = 0.065
Optical character biaxial positive
Axis angle 2V = 60 ° (measured); 50 ° (calculated)

Earlandite is an extremely rare mineral from the mineral class of organic compounds . It crystallizes in the monoclinic crystal system with the composition Ca 3 (C 6 H 5 O 7 ) 2 · 4H 2 O and is therefore chemically a calcium citrate , i.e. H. the calcium salt of citric acid .

Earlandite has only been known to have bulbous or kidney-shaped, polycrystalline mineral aggregates , whereby they have a characteristic, rough surface. The size of the aggregates found so far was around 1.5 mm. Larger crystal groups or single crystals have not yet become known. Due to the rarity of these minerals, many parameters, such as hardness or fracture behavior, have not yet been determined.

Etymology and history

Earlandite was first found during the Scottish National Antarctic Expedition (1902-1904) and described by Arthur Earland , a British oceanographer. The exact analysis of the mineral and its classification were only carried out in 1936 by FA Bannister and MH Hey. They then named the mineral after the first discoverer.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the earlandite belonged to the mineral class of "organic compounds" and there to the department of "salts of organic acids", where together with abelsonite , calclacite , dashkovaite , formicaite , hoganite , Julienit , Kafehydrocyanit , Mellit and Paceit the "Mellit-Julienit-Gruppe" with the system no. IX / A.02 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 earlandite to the class of "organic compounds" and there to the department of "salts of organic acids". This division is, however, further subdivided according to the salt-forming acid, so that the mineral can be found according to its composition in the sub-division of " Benzene salts", where it is the only member of the unnamed group 10.AC.10 . It should be noted, however, that earlanditol is neither a derivative of benzene nor an aromatic compound .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the earlandite to the class of "organic minerals" and the department of the same name. Here he is to be found as the only member of the unnamed group 50.02.02 within the subdivision of " Salts of organic acids (mellitates, citrates, cyanates and acetates) ".

Education and Locations

To date, the exact formation of earlandite has not yet been clarified. What is certain, however, is that it is caused by biomineralization , as the formation of citric acid or its salts is linked to biological processes (see → Citric acid cycle ). Even if the solubility of calcium citrate in cold water is poor, the formation of earlandite in the deep sea sediments is remarkable.

Earlandite specimens were found that had grown on the shells of foraminifera or that had formed in the drill holes of deep-sea worms. The latter is used as evidence that earlandite forms in the sediment and is not brought into the sediment by external influences. Minerals typically associated with earlandite are gypsum and weddellite .

The only known site (as of 2013) for earlandite is the Weddell Sea in western Antarctica . Here it was found at the coordinates 71 ° 22 ′  S , 16 ° 34 ′  W at a depth of 2580 m in the corresponding deep-sea sediments.

Crystal structure

Earlandite crystallizes monoclinically with the lattice parameters a  = 30.94  Å ; b  = 5.93 Å; c  = 10.56 Å and β = 93.7 ° and 4 formula units per unit cell . Due to the rarity and the fact that earlandite only contains polycrystalline aggregates, no further data on the crystal structure are available.

The chemical formula of earlandite can best be represented as Ca 3 [CH 2 (COO) -CHOH (COO) -CH 2 (COO)] 2 · 4H 2 O (see the structural formula of calcium citrate ), as it is often used in the The idealized empirical formula Ca 3 (C 6 H 5 O 7 ) 2 · 4H 2 O used in the literature makes no statement about the structure of the citrate anion.

use

While there are many uses for calcium citrate , these are only hypothetical due to the extreme rarity of earlandite for the mineral.

See also

literature

  • Arthur Earland, FA Bannister, MH Hey: Foraminifera, Part IV. Additional Records from the Weddell Sea sector from material obtained by the SY "Scotia" . In: Discovery Reports . tape XIII , 1936, p. 1–76 ( rruff.info [PDF; 742 kB ; accessed on April 7, 2018]).

Web links

Individual evidence

  1. ↑ a b c d 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.  721 .
  2. ↑ a b c d e f g Mindat - Earlandite
  3. ↑ Earlandite . 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; 64  kB ; accessed on April 7, 2018]).
  4. ↑ Arthur Earland, FA Bannister, MH Hey: Foraminifera, Part IV. Additional Records from the Weddell Sea sector from material obtained by the SY "Scotia" . In: Discovery Reports . tape XIII , 1936, p. 1–76 ( rruff.info [PDF; 742 kB ; accessed on April 7, 2018]).
  5. ^ New Mineral Names . In: Academy of Natural Sciences of Philadelphia (Ed.): American Mineralogist . tape  22 , no. 1 , 1937, p. 70–72 ( minsocam.org [PDF; 400 kB ; accessed on April 7, 2018]).
  6. ↑ Steve Weiner, Patricia M. Dove: An Overview of Biomineralization Processes and the Problem of the Vital Effect . In: Reviews in Mineralogy and Geochemistry . tape 54 , no. 1 , January 3, 2003, p. 1–29 , doi : 10.2113 / 0540001 ( mcgill.ca [PDF; 1.6 MB ; accessed on April 7, 2018]).
  7. ↑ Find location list for earlandite at the Mineralienatlas and at Mindat