Evenkit

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Evenkit
Evenkite-444375.jpg
Colorless Evenkit unit from Dubník , Slovakia
General and classification
chemical formula C 23 H 48
Mineral class
(and possibly department) 		Organic compounds - hydrocarbons
System no. to Strunz
and to Dana 		10.BA.50 ( 8th edition : IX / B.01)
50.03.06.01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pbcm (No. 57)Template: room group / 57
Lattice parameters a  = 7.474 (1)  Å ; b  = 4.980 (1) Å; c  = 65.85 (3) Å
Formula units Z  = 4
Twinning polysynthetic twins
Physical Properties
Mohs hardness 1
Density (g / cm 3 ) measured: 0.920; calculated: [0.926]
Cleavage completely after {001}
Break ; Tenacity not applicable (waxy consistency)
colour colorless, white, light yellow, green
Line color White
transparency transparent to translucent
shine Wax gloss
Crystal optics
Refractive indices n α  = 1.504
n β  = 1.504
n γ  = 1.553
Birefringence δ = 0.049
Optical character biaxial positive
Other properties
Chemical behavior easily soluble in ether

Evenkit (chemical name Tetracosane ) is a very rarely occurring mineral from the mineral class of organic compounds and the division of nitrogen-free hydrocarbons . It crystallizes in the orthorhombic crystal system with the chemical composition C 23 H 48

Evenkit develops tabular and twinned pseudo-hexagonal crystals , but is also found in the form of granular to coarse mineral aggregates . In its pure form, Evenkit is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and, due to foreign admixtures, take on a light yellow to greenish color, the transparency decreasing accordingly. However, its line color is always white.

Etymology and history

Evenkit was named after its type locality Evenki (today the Evenki Autonomous Okrug ) in the Russian region of Krasnoyarsk (Siberia), where it was first found and described by AV Skropyshev in 1953.

Type material of the mineral is kept in the Mineralogical Museum of the St. Petersburg State University in Russia (Catalog No. 924-1 / 1–924-1 / 3).

classification

Already in the outdated, but partly still in use systematics of minerals according to Strunz (8th edition) , the Evenkit belonged to the mineral class of "organic compounds" and to the department of "nitrogen-free hydrocarbons", where it was the only member of the group "chain structures" with the system no. IX / B.01 formed.

The department designation was not adopted in the 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA) . The mineral is there as the only member in the unnamed group 10.BA.50 within the also unnamed "A." of the "Hydrocarbons" department.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Evenkit to the class and department of the same name of "organic minerals". Here he is to be found as the only member in the unnamed group 50.03.06 within the sub-section "Salts of organic acids (hydrocarbons)".

Crystal structure

Evenkit crystallizes orthorhombically in the space group Pbcm (space group no. 57) with the lattice parameters a  = 7.474 (1)  Å ; b  = 4.980 (1) Å and c  = 65.85 (3) Å and 4 formula units per unit cell . Template: room group / 57

properties

Chemism and chemical properties

Idealized chemical structure of Evenkit

Chemically speaking, Evenkit is a linear, aliphatic hydrocarbon or paraffin . The mean chemical composition is generally given as (CH 3 ) 2 (CH 2 ) 22 or, more simply, as C 24 H 50 , which corresponds to the chemical substance tetracosane . However, it should be noted that it is only a sum formula. In fact, Evenkit does not have a uniform chemical structure. The chain lengths of the molecules can be between 20 and 31 carbon atoms. For the type material, an average chain length of 24 to 25 carbon atoms was determined by GC-MS .

According to more recent analyzes by Platonova and Kotel'nikova in 2004, the simplified formula is given as C 23 H 48 .

Evenkit is readily soluble in ether .

Physical Properties

Aliphatic hydrocarbons with chain lengths of around 25 carbon atoms have a waxy consistency, similar to ozokerite . Accordingly, Evenkit is one of the softest minerals with a Mohs hardness of 1. Nevertheless, a perfect, mica-like cleavage towards the basal surface {001} can be observed in Evenkite crystals .

The melting point of Evenkit is around 49 to 51 ° C. With a measured density of 0.920 g / cm 3 (according to other sources also 0.873 g / cm 3 ) Evenkit is one of the lightest minerals. Correspondingly, fragments can float on the water.

Education and Locations

The exact educational conditions are not known at the moment, but a secondary education is suspected . At its type locality Evenkit was in quartz - geodes discovered, resulting in a narrow ore body in the contact zone between tuff and lava on the lower Tunguska ( Nizhnyaya Tunguska ). As accompanying minerals may include chalcedony , calcite , chalcopyrite , galena , pyrite , pyrrhotite and sphalerite occur.

In addition to its type locality (as of 2014), other known sites are only Curbans , Orpierre and Serres (Hautes-Alpes) in France, the Ilímaussaq massif near Narsaq on Greenland and Dubník , Ladomírov and Merník in Okres Prešov in Slovakia.

See also

literature

  • AV Skropyshev: A paraffin from a polymetallic vein . In: Doklady Akademii Nauk SSSR . tape 88 , 1953, pp. 717–719 (Russian, rruff.info [PDF; 809 kB ; accessed on January 3, 2017]).
  • EN Kotel'nikova, SK Filatov, NV Chukanov: Evenkite: symmetry, chemical composition, identification and thermal behavior . In: Zapiski Vserossijskogo Mineralogicheskogo Obshchestva . tape 133 , 2004, chap. 3 , p. 80–92 (Russian, rruff.info [PDF; 943 kB ; accessed on January 3, 2017] with a brief description in English).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 282 .

Web links

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

Individual evidence

  1. ↑ a b c d e f NV Platonova, EN Kotel'nikova: Synthesis of the organic mineral evenkite . In: Geology of Ore Deposits . tape 49 , December 2007, chap. 7 , p. 638-640 , doi : 10.1134 / S1075701507070227 . (Original in: Zapiski Vserossijskogo Mineralogicheskogo Obshchestva Volume 133, Chapter 3, 2004, pp. 80–92; PDF 943 kB , Russian with a brief description in English)
  2. ↑ a b c d e Evenkite . 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 January 3, 2017]).
  3. ↑ a b c d Mindat - Evenkite
  4. ^ A b c K. Yagi, Michael Fleischer : New mineral names. Evenkite . In: American Mineralogist . tape 40 , 1955, pp. 367–370 ( rruff.info [PDF; 272 kB ; accessed on January 3, 2017]).
  5. ^ JE Spangenberg, M. Meisser: Geochemistry of the organic mineral evenkite in sptarian concretions in the Oxfordian marls of the French Alps . In: Mineralogical Magazine; Geology of Ore Deposits 1998 . 62A, p. 1436–1437 ( minersoc.org [PDF; 102 kB ; accessed on January 3, 2017]).
  6. ^ IMA / CNMNC List of Mineral Names; July 2015 (PDF 1.5 MB)
  7. ↑ a b c Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  799 (first edition: 1891).
  8. ↑ Find location list for Evenkit in the Mineralienatlas and Mindat