Moganite

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Moganite
Mogánite.jpg
Honey-yellow Mogánite aggregate from the type locality Mogan on the Canary Islands
General and classification
other names
  • IMA 1999-035
  • Moganite
  • Silica-G (original English description 1976)
chemical formula SiO 2
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DA.20 ( 8th edition : IV / D.01)
January 75, April 02
Similar minerals microcrystalline quartz ( chalcedony )
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group I 2 / a (No. 15, position 3)Template: room group / 15.3
Lattice parameters a  = 8.76  Å ; b  = 4.88 Å; c  = 10.71 Å
β  = 90.1 °
Formula units Z  = 12
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) 2.52 to 2.58
Cleavage not defined
Break ; Tenacity not defined
colour colorless, white, gray, brownish-white to gray-brown
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.524
n γ  = 1.531
Birefringence δ = 0.007
Optical character biaxial

Mogánite is a common mineral from the silicic acid family within the mineral class of " oxides and hydroxides ". It crystallizes in the monoclinic crystal system with the chemical composition SiO 2 . The microcrystalline aggregates contain two to three percent by weight H 2 O .

Visible needle-like to hair-like crystals of mogánite have so far only been described from agates from a deposit in Mongolia . Otherwise, mogánite forms fibrous aggregates of submicroscopic strip-shaped crystals.

Etymology and history

Mogánit was discovered in 1976 by OW Flörke, B. Jones, and H.-U. Schmincke in volcanic rocks ( rhyolitic ignimbrites ) on Gran Canaria , Spain and first described in 1984 by Flörke and U. Giese as the new mineral mogánite. The authors named it after the type locality Mogán on Gran Canaria, Las Palmas Province , Canary Islands , Spain. The status as an independent mineral was controversial for a long time, until 1999 mogánite was also recognized as a mineral by the International Mineralogical Association (IMA).

In older publications, the mineral name can usually be found in the spelling Moganit (without acute ), which does not, however, correspond to the specifications for mineral naming of the IMA, according to which, for example, minerals that were named after a geographical location, care must be taken that the spelling of the name corresponds to that at the type locality. The inconsistent spelling of their names for many minerals was corrected with the publication “Tidying up Mineral Names: an IMA-CNMNC Scheme for Suffixes, Hyphens and Diacritical marks” in 2008 and the Mogánit has been spelled internationally since then with the associated acute.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the mogánite belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with metal: oxygen = 1: 2", where together with coesite , cristobalite , Lechatelierite , melanophlogite , opal , quartz , seifertite , stishovite and tridymite the "quartz series" with the system no. IV / D.01 .

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also assigns mogánite to the class of "oxides and hydroxides" and there into the department of "oxides with the molar ratio of metal: oxygen = 1: 2 and comparable “. However, this is further subdivided according to the relative size of the cations involved and the type of linkage of the oxide complex. An exception are the minerals of the silica family with small cations, which form an independent subdivision and which also includes mogánite , which is the only member of the unnamed group 4.DA.20 .

In contrast to Strunz's systematics, the systematics of minerals according to Dana assigns mogánite to the class of " silicates " and there in the department of " framework silicates ". Here it can be found together with Coesit in the unnamed group 75.01.04 within the subdivision " 75.01 Tectosilicates: tetrahedral Si lattice, SiO 2 with [4] -coordinated Si ".

Crystal structure

Crystal structure; Oxygen atoms (O 2 ) red

Mogánite crystallizes monoclinically in the space group I 2 / a (space group no. 15, position 3) with the lattice parameters a  = 8.76  Å ; b  = 4.88 Å; c  = 10.71 Å and β = 90.1 ° and 12 formula units per unit cell . Template: room group / 15.3

The structure of mogánite is closely related to that of quartz . Silicon is surrounded by 4 oxygen atoms in such a way that the oxygen anions lie on the corners of a tetrahedron with the Si 4+ cation in the center . These SiO 4 tetrahedra are connected to one another via common oxygen (tetrahedron corners) to form a framework structure.

The mogánite structure can be derived from the quartz structure as periodic twinning according to the Brazilian law on the unit cell level. The moganite structure is built up from a periodically alternating sequence of right and left quartz, which are only one unit cell thick and grown together along the (101) surface.

Modifications and varieties

Mogánite is a modification of SiO 2 . It is metastable at all pressures and temperatures and converts to α-quartz over geological time periods .

At approx. 570 K the monoclinic α-mogánite transforms into the orthorhombic β-mogánite.

As Lutecin or Lutecit a fibrous will variety of Mogánits denotes the closely adherent to chalcedony or quartz occurs.

Education and Locations

White mogánite on brown chalcedony , pseudomorphic after Turritella (genus of marine snails)

Moganite found grown in most microcrystalline siliceous rocks ( Chert to over 75%, Feuerstein 13-17%, chert , etc.) and microcrystalline quartz varieties ( agate , chalcedony 5-20%), the younger are over 100 million years. However, almost pure moganite is rare and the mineral database "mindat.org" lists for moganite world's only about 36 localities in (as of 2014), so among other things in the "poor relief Mine" at Ullersreuth in Thuringia, in Ördögorom in Hungary , on Gran Canaria and Lulworth Cove in England .

Mogánite separates out of basic solutions at low temperatures . Concentrations of more than 20 percent by weight of mogánite in silicic acid concretions indicate formation in an evaporitic environment.

See also

literature

  • OW Flörke, JB Jones, H.-U. Schmincke: A new microcrystalline silica from Gran Canaria . In: Journal of Crystallography . tape 143 , 1976, pp. 156-165 .
  • OW Flörke, U. Flörke, U. Giese: Moganite, a new microcrystalline silica-mineral . In: New Yearbook for Mineralogy Treatises . tape 149 , 1984, pp. 325-336 .
  • Pete J. Dunn, Michael Fleischer , Richard H. Langley, James E. Shigley, Janet A. Zilczer: New Mineral Names - Mogánite . In: American Mineralogist . tape 70 , 1985, pp. 871-881 ( minsocam.org [PDF; 1.4 MB ; accessed on July 30, 2017]).
  • John Leslie Jambor , Ernst AJ Burke: New Mineral Names - Monoclinic polymorph of SiO 2 . In: American Mineralogist . tape 75 , 1990, pp. 1435 ( minsocam.org [PDF; 824 kB ; accessed on July 30, 2017]).
  • John Leslie Jambor, Edward S. Grew: New Mineral Names - Lutecite . In: American Mineralogist . tape 78 , 1993, p. 236 ( minsocam.org [PDF; 716 kB ; accessed on July 30, 2017]).
  • John Leslie Jambor, Ernst AJ Burke, Edward S. Grew, Jacek Puziewicz: New Mineral Names - Mogánite . In: American Mineralogist . tape 78 , 1993, p. 677-678 ( minsocam.org [PDF; 809 kB ; accessed on July 30, 2017]).
  • Peter J. Heaney, Jeffrey E. Post: Evidence for at I2 / a to Imab phase transition in the silica polymorph Mogánite at ~ 570 K . In: American Mineralogist . tape 86 , 2001, p. 1358–1366 ( arizona.edu [PDF; 1.6 MB ; accessed on July 30, 2017]).

Web links

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

Individual evidence

  1. ↑ Webmineral - Moganite (mineral database , English)
  2. ^ A b c 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.  205 .
  3. ↑ a b c Pete J. Dunn, Michael Fleischer, Richard H. Langley, James E. Shigley, Janet A. Zilczer: New Mineral Names - Mogánite . In: American Mineralogist . tape 70 , 1985, pp. 871-881 ( minsocam.org [PDF; 1.4 MB ]).
  4. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  5. ↑ a b Mindat - Mogánite (mineral database , English)
  6. ^ A b John Leslie Jambor, Ernst AJ Burke, Edward S. Grew, Jacek Puziewicz: New Mineral Names - Mogánite . In: American Mineralogist . tape 78 , 1993, p. 677–678 ( minsocam.org [PDF; 81 kB ]).
  7. ^ A b John Leslie Jambor, Edward S. Grew: New Mineral Names - Lutecite . In: American Mineralogist . tape 78 , 1993, p. 236 ( minsocam.org [PDF; 72 kB ; accessed on July 30, 2017]).
  8. ↑ OW Flörke, JB Jones, H.-U. Schmincke: A new microcrystalline silica from Gran Canaria . In: Journal of Crystallography . tape 143 , 1976, pp. 156-165 .
  9. ^ John Leslie Jambor, Ernst AJ Burke: New Mineral Names - Monoclinic polymorph of SiO 2 . In: American Mineralogist . tape 75 , 1990, pp. 1435 ( minsocam.org [PDF; 83 kB ]).
  10. ↑ Ernest H. Nickel , Joel D. Grice: The IMA Commission on New Minerals and Minerala Names: Procedures and Guidelines on Mineral Nomenclature . In: The Canadian Mineralogist . tape  36 , 1998 ( edu.au [PDF; 328 kB ] from p. 8).
  11. ^ Ernst AJ Burke: Tidying up Mineral Names: an IMA-CNMNC Scheme for Suffixes, Hyphens and Diacritical marks . In: Mineralogical Record . tape 39 , no. 2 , March 2008 ( edu.au [PDF; 2.7 MB ]).
  12. ↑ IMA / CNMNC List of Mineral Names 2009 (PDF 1.8 MB); For the current mineral list, see the IMA website
  13. ↑ a b c d Peter J. Heaney, Jeffrey E. Post: Evidence for at I2 / a to Imab phase transition in the silica polymorph Mogánite at ~ 570 K . In: American Mineralogist . tape 86 , 2001, p. 1358–1366 ( arizona.edu [PDF; 1.5 MB ]).
  14. ↑ Peter J. Heaney, Jeffrey E. Post: The widespread distribution of a novel silica polymorph in microcrysalline quartz . In: Science . tape 255 , 1992, pp. 441-444 .
  15. ↑ Mindat - Localities for Mogánite