Aenigmatite

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Aenigmatite
Aenigmatite - Mineralogical Museum Bonn1.jpg
Aenigmatite crystal from the sodalite syenite from Kangerlussuaq , Greenland
General and classification
chemical formula Na 2 (Fe 2+ 4 Ti) Fe 2+ [O 2 | Si 6 O 18 ]
Mineral class
(and possibly department) 		Silicates and germanates - chain and band silicates
System no. to Strunz
and to Dana 		9.DH.45 ( 8th edition : VIII / D.07)
69.02.01a.01
Similar minerals basaltic hornblende , Rhoenite
Crystallographic Data
Crystal system Triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 10.41  Å ; b  = 10.81 Å; c  = 8.93 Å,
α  = 104.9 °; β  = 96.9 °; γ  = 125.3 °
Formula units Z  = 2
Twinning Rotational twins according to (01 1 ) or [010] (pseudomonoclinic cell), polysynthetic twins
Physical Properties
Mohs hardness 5.5
Density (g / cm 3 ) measured: 3.81; calculated: 3.84
Cleavage good according to {010} and {100}, slit angle of ~ 66 °, an important difference to the amphiboles
Break ; Tenacity uneven to shell-like; brittle
colour velvet black
Line color red-brown
transparency translucent to opaque
shine Glass gloss, fat gloss
Crystal optics
Refractive indices n α  = 1.780 to 1.800
n β  = 1.800 to 1.820
n γ  = 1.870 to 1.900
Birefringence δ = 0.090 to 0.100
Optical character biaxial positive
Axis angle 2V = measured: 27 to 55 °; calculated: 56 to 60 °
Pleochroism strong (absorbs all colors except red): X = yellow-brown; Y = red brown; Z = dark brown to black
Other properties
Chemical behavior attacked by hydrochloric acid (HCl)
Special features The optical axis plane and the twin seam roughly halve the obtuse angle of the cracks

The mineral aenigmatite is a relatively rare chain silicate from the mineral class of silicates . It crystallizes in the triclinic crystal system with the chemical composition Na 2 (Fe 2+ 4 Ti) Fe 2+ [O 2 | Si 6 O 18 ] and usually develops short, prismatic crystals of black color with red-brown streak color . Thin lamellae are brownish translucent.

With Wilkinsonit aenigmatite forms a mixed batch .

Etymology and history

Aenigmatite and its type locality , the Ilimaussaq intrusion in the vicinity of the Kangerlussuaq fjord in southwest Greenland , was first described in 1865 by August Breithaupt (1791–1873). He named the mineral after the Greek word αἴνιγμα ("the riddle") to indicate its originally unexplained chemical composition.

Type material of the mineral is in the geoscientific collections of the TU Bergakademie Freiberg under the collection no. 28614 , 29166 and 29167 . It is a small stage and material in tubes.

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , the aenigmatite belonged to the mineral class of "silicates and germanates" and there to the department of "chain and band silicates (inosilicates)", where it was named after the "aenigmatite group" with the system -No. VIII / D.07 and the other members Deerit , Hainit , Howieit , Magbasit , Rhönit and Tinaksit formed.

In the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this form of Karl Hugo Strunz's system , the mineral received the system and mineral number. VIII / F.14-20 . In the "Lapis system" this also corresponds to the section "Chain and band silicates", where aenigmatite together with Addibischoffit , Dorrit , Høgtuvait , Khesinit , Krinovit , Kuratit , Makarochkinit , Rhönit , Serendibit , Warkit , Welshit and Wilkinsonit form the "Aenigmatit- Group "forms (as of 2018).

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also classifies the aenigmatite in the “chain and band silicates” department. This is, however, further subdivided according to the structure of the chains, so that the mineral can be found according to its crystal structure in the subsection "Chain and band silicates with 4-periodic single chains, Si 4 O 12 ", where it can be found together with Baykovit , Dorrit, Høgtuvait , Khmaralith , Krinovit, Makarochkinit, Rhönit, Sapphirin , Serendibit, Welshit and Wilkinsonit form the unnamed group 9.DH.45 .

The systematics of minerals according to Dana also assigns the aenigmatite to the class of "silicates and germanates", but there in the more finely subdivided division of "chain silicates: chains with side branches or loops". Here he is the namesake of the group "aenigmatite and related species (aenigmatite subgroup)" with the system no. 69.02.01a and the other members Dorrit, Høgtuvait, Krinovit, Rhönit, Serendibit, Welshit, Wilkinsonit and Makarochkinit can be found in the subsection " Chain silicates: chains with side branches or loops with P> 2 ".

Crystal structure

Aenigmatite crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 10.41  Å ; b  = 10.81 Å; c  = 8.93 Å; α = 104.9 °; β = 96.9 ° and γ = 125.3 ° as well as 2 formula units per unit cell . Template: room group / 2

Modifications and varieties

So far, no further modifications of the compound Na 2 (Fe 2+ 4 Ti) Fe 2+ [O 2 | Si 6 O 18 ] are known.

As Cossyrit one is iron-rich variety of aenigmatite with additional Ti and Fe 3+ called ions.

Education and Locations

Aenigmatite crystal on Sanidin from Água de Pau , São Miguel, Azores (field of view 4.84 mm)

Aenigmatite usually forms in light, sodium- accentuated (alkaline) magma rocks . These include:

Socialized is aenigmatite especially with Aegirin , Arfvedsonit and Riebeckite , but also albite , anorthoclase , Astrophyllit , pyroxene , fayalite , Hedenbergit and ilmenite may join.

As a rather rare mineral formation, aenigmatite can in part be abundant at different sites, but overall it is not very common. Around 170 sites for aenigmatite have been documented worldwide (as of 2020). In addition to its type locality Ilimaussaq, the mineral was also found in Greenland at Igaliku , Nunarssuit and Quagdlimiut in the Kitaa district and at Kangerlussuaq and Kialineq Bay in the Tunu district .

Other localities are Tasmania in Australia, the northern and southwestern regions of Cameroon , several regions of Canada , Mianning in China, Pantelleria in Italy, the Japanese island of Honshu , the peninsula Ampasindava of Madagascar , the Mongolian Altai Mountains , at Aris in the Namibian region Khomas , New Zealand , the Nigerian region of Agadez , Kangwŏn-do in North Korea, several regions of the Norwegian provinces of Telemark and Vestfold , the Azores in Portugal, several regions of the Russian Kola Peninsula , the island of Ascension , which belongs to St. Helena, Ascension and Tristan da Cunha , Gyeongsangbuk-do in South Korea, in South Yemen , at the Ngorongoro Crater in Tanzania, Strathclyde in Great Britain, Ukraine , Mecsek in Hungary and several regions in the United States .

See also

literature

  • August Breithaupt : Mineralogical Studies. 29. Kölbingite. Ainigmatite . In: Berg- und Hüttenmännische Zeitung . tape 24 , 1865, pp. 397–398 ( rruff.info [PDF; 243 kB ; accessed on January 13, 2020]).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 241 .
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 730 (first edition: 1891).

Web links

Commons : Aenigmatite  - 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.  643 .
  2. ^ David Barthelmy: Aenigmatite Mineral Data. In: webmineral.com. Retrieved January 13, 2020 .
  3. ↑ a b c d Aenigmatites . 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; 73  kB ; accessed on January 13, 2020]).
  4. ↑ a b c d e Aenigmatite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 13, 2020 .
  5. ↑ Type mineral catalog - Aenigmatite. In: typmineral.uni-hamburg.de. University of Hamburg , December 8, 2017, accessed on January 13, 2020 .
  6. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  7. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1816 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed January 13, 2020 .
  8. ↑ Localities for Aenigmatite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 13, 2020 .
  9. ↑ Find location list for aenigmatite in the Mineralienatlas and Mindat , accessed on January 13, 2020.