Ikait

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Ikait
General and classification
other names
  • Hydrocalcite
  • IMA 1962-005
chemical formula Ca [CO 3 ] • 6H 2 O
Mineral class
(and possibly department) 		Carbonates and nitrates (formerly carbonates, nitrates and borates)
System no. to Strunz
and to Dana 		5.CB.25 ( 8th edition : V / D.01)
01/15/04
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 8.79  Å ; b  = 8.31 Å; c  = 11.02 Å
β  = 110.5 °
Formula units Z  = 4
Physical Properties
Mohs hardness not defined
Density (g / cm 3 ) measured: 1.77; calculated: [1,833]
Cleavage not defined
colour chalk white
Line color White
transparency Please complete!
shine Please complete!
Crystal optics
Refractive indices n α  = 1.455
n β  = 1.538
n γ  = 1.545
Birefringence δ = 0.090
Optical character biaxial negative
Axis angle 2V = 45 ° (measured); 30 ° (calculated)
Other properties
Chemical behavior dehydrates to calcite at over 8 ° C

Ikaite is a very rarely occurring mineral from the mineral class of " carbonates and nitrates ". It crystallizes in the monoclinic crystal system with the composition Ca [CO 3 ] · 6H 2 O, so it is chemically a water-containing calcium carbonate .

Since Ikaite is only chemically stable up to about 8 ° C and above it changes into calcite due to the loss of crystal water , there are predominantly only pseudomorphoses from calcite to Ikait, which are also known as "glendonite". Real Ikaite crystals have a tabular habit and are usually only a few millimeters in size. However, there are also known submarine, columnar mineral aggregates several decimeters thick and several meters high with a porous bark made of small, shiny icaite crystals.

Etymology and history

Ikait was first discovered in the Ikkafjord (also Ikka Firth or Ika Fjord ), more precisely in the local "Ikka-Grønnedal complex" near Ivittuut in Greenland and described in 1963 by the Danish mineralogist Hans Pauly , who named the mineral after its type of locality .

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of ikaite belonged to the mineral class of "carbonates, nitrates and borates" and then to the Department of "water containing carbonates without foreign anions " where he along with Barringtonit , Hellyerit , Lansfordit , Monohydrocalcite and nesquehonite the "nesquehonite-lansfordite group" with the system no. V / D.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), assigns Ikaite to the new class of "carbonates and nitrates" (the borates form a separate class here). There the mineral still belongs to the category of “carbonates without additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the element groups of the metals, so that the mineral can be found in the sub-section “With large cations (alkali and alkaline earth carbonates)”, where it is the only member, according to its composition forms the unnamed group 5.CB.25 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Ikait, like the outdated Strunzian system, to the common class of “carbonates, nitrates and borates” and there to the division of “hydrous carbonates”. Here he is to be found as the only member of the unnamed group 01/15/04 within the sub-section " Hydrogen carbonates with A + (XO 3 ) · x (H 2 O)".

Crystal structure

Ikait crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 8.79  Å ; b  = 8.31 Å; c  = 11.02 Å and β = 110.5 ° and 4 formula units per unit cell . Template: room group / 15

properties

Ikaite is chemically unstable and dehydrated at over 8 ° C, which means that it loses its water of crystallization and changes into the mineral calcite .

Modifications and varieties

Glendonite from the Russian Kola Peninsula (size: 10.3 × 7.7 × 5.9 cm)

Glendonite is the best known pseudomorphism from calcite after Ikait. Similar pseudomorphoses from calcite to Ikait are also known under the names fundylite , jarrowit or thinolite , the latter actually denoting a pseudomorphism from calcite to gaylussite .

A very popular, but extremely rare variety are the so-called "Pineapple Opals" (also Opal Pineapple ), hedgehog or pineapple-shaped pseudomorphs from Opal to Ikait, which have so far only been found in opal fields near White Cliffs and Andamooka in Australia.

Education and Locations

Ikait forms in seawater under anaerobic conditions in periglacial and glaciomarine environments, i.e. geological areas formed or influenced by frost and glaciers , rich in organic matter.

As a very rare mineral formation, Ikaite has so far only been detected in a few mineral samples and fewer than 10 sites are known to date (as of 2013). Its type locality Ikkafjord is the only known site in Greenland so far , but where the largest columnar mineral aggregates have been found with a length of 10 meters.

Other locations are among others

  • the Hunter Valley in New South Wales, Australia, where glendonite pseudomorphs up to eight inches in size have been found.
  • the Koda Cave near Beroun in the Czech region of Central Bohemia
  • Shiowakka in Tokachi Sub-prefecture on the Japanese island of Hokkaido
  • the Olenitsa River , which flows into the White Sea near the Russian Kola Peninsula and is also known for its hedgehog or star-shaped glendonite pseudomorphoses.
  • the Natronsee Mono Lake in the US state of California.

The Ikait find in the Antarctic, namely in Adélieland , the Bransfield Strait and the Weddell Sea , is considered to be an important discovery, possibly of great importance in the global carbon cycle. The mineral was discovered there in two Antarctic expeditions in 2006 and 2007 by a team of scientists led by Gerhard Dieckmann .

See also

literature

  • H. Pauly: Ikait, nyt mineral der danner skaer . In: 'Naturens Verden (Copenhagen) . June 1963, p. 168-192 (Danish).
    • H. Pauly: Ikaite, a new mineral from Greenland . In: Arctic . tape 16 , 1963, pp. 263-264 (English).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 591 (first edition: 1891).

Web links

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

Individual evidence

  1. ↑ a b c d e 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.  305 .
  2. ↑ Ikaite . 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; 66  kB ; accessed on April 16, 2018]).
  3. ↑ a b c d e f g h i Mindat - Ikaite
  4. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  581 (first edition: 1891).
  5. ↑ Mindat - type locality Ikka-Grønnedal complex, Ikka Firth (Ika fjord), Ivittuut (Ivigtut), Arsuk Firth, Arsuk, Kitaa (West Greenland) Province, Greenland
  6. ↑ a b scinexx - The Knowledge Magazine: Climate: An important mineral discovered in the sea ice. Ikait with great importance in the global carbon cycle
  7. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  582 (first edition: 1891).
  8. ↑ White Cliffs Opal
  9. ↑ Mindat - Pineapple Opal
  10. ↑ Mindat - Number of localities for Ikait
  11. ↑ a b c The Giant Crystal Project Site - Ikaite ( Memento of November 8, 2012 in the Internet Archive )