Lepidocrocite

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Lepidocrocite
Lepidocrocite-170212.jpg
leafy lepidocrocite from the "Alto das Quelhas do Gestoso Mines" near Manhouce ( São Pedro do Sul ), Portugal (image size 1.5 mm)
General and classification
other names
chemical formula γ-Fe 3+ O (OH)
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.FE.15 ( 8th edition : IV / F.06)
01/06/02/02
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Cmc 2 1 (No. 36)Template: room group / 36
Lattice parameters a  = 3.08  Å ; b  = 12.50 Å; c  = 3.87 Å
Formula units Z  = 4
Frequent crystal faces tabular after {010}
Physical Properties
Mohs hardness 5
Density (g / cm 3 ) measured: 4.09; calculated: 3.96
Cleavage completely [010]
Break ; Tenacity uneven, mussel-like
colour dark red to red brown
Line color reddish to brownish
transparency transparent to opaque
shine weak metallic luster to diamond luster, silk luster
Crystal optics
Refractive indices n α  = 1.940
n β  = 2.200
n γ  = 2.510
Birefringence δ = 0.570
Optical character biaxial negative
Axis angle 2V = measured: 83 °; calculated: 84 °
Pleochroism strong: X = b = yellow; Y = c = dark red-orange; Z = a = darker red-orange

Lepidocrocite (also ruby mica ) is a seldom occurring mineral from the mineral class of " oxides and hydroxides " with the chemical composition γ-Fe 3+ O (OH) and is therefore chemically iron (III) hydroxide oxide .

Lepidocrocite crystallizes in the orthorhombic crystal system and develops mostly tabular to short prismatic crystals up to about 2 mm in size from dark red to red-brown in color with reddish-brown streak color , which occasionally form rosette-shaped mineral aggregates . Radial-needle, granular, fibrous and earthy-massive aggregates are also known. On the crystal surfaces of weak metal shows up diamond gloss , fine aggregates noble contrast silky shine.

Etymology and history

Lepidocrocite was first discovered around the same time in the Eisenzecher Zug mine near Eiserfeld (Siegen) in Germany and at the Zlaté Hory (German: Zuckmantel ) in the Czech Republic. The mineral was first described in 1813 by Johann Christoph Ullmann , who named it due to its occasional leafy to needle-like-fibrous crystal formation after the Greek words λεπιδιον for "scaly" and κρόκη for "thread" or "tissue".

Ullmann described in 1814 next to the Lepidokrokit as part of limonite and a "ruby red micaceous iron " (short ruby mica ), which he described as Pyrrhosiderit (Greek, fire-colored 'and σίδηρος for, iron' Πύρρος for) described and compared with the common micaceous iron oxide, where he went into detail on their distinguishing features. Hausmann , however, equates pyrrhosiderite with lepidocrocite.

classification

In the outdated, but still in use, 8th edition of the mineral classification according to Strunz , the lepidocrocite belonged to the mineral class of "oxides and hydroxides" and there to the department of "hydroxides and oxidic hydrates", where it together with akaganeit , boehmite , diaspore , feitknechtite , feroxyhyte , Goethite , groutite , manganite , sword mannite and tsumgallite the “Akaganeit group” with the system no. IV / F.06 .

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 the lepidocrocite to the class of "oxides and hydroxides", but in the more finely divided section of "hydroxides (without V or U) ”. This is further subdivided according to the possible presence of hydroxide ions or water of crystallization and the crystal structure, so that the mineral according to its composition and structure is classified in the sub-section “Hydroxides with OH, without H 2 O; Layers of edge-linked octahedra "can be found, where only together with boehmite the" boehmite group "with the system no. 4.FE.15 forms.

The systematics of minerals according to Dana also assigns the lepidocrocite to the class of "oxides and hydroxides" and there in the department of "hydroxides and hydroxide-containing oxides". Here it is together with boehmite and guyanaite in the " boehmite group " with the system no. 06.01.02 to be found in the subsection “Hydroxides and hydroxide-containing oxides with the formula: X 3+ OOH”.

Crystal structure

Crystal structure of lepidocrocite

Lepidocrocite crystallizes isotypically with boehmite in the orthorhombic crystal system in the space group Cmc 2 1 (space group no. 36) with the lattice parameters a  = 3.08  Å ; b  = 12.50 Å and c  = 3.87 Å and 4 formula units per unit cell . Template: room group / 36

The crystal structure of lepidocrocite is composed of double layers of edge-sharing, distorted Fe (O, OH) 6 - octahedra which together form chains parallel to the c-axis [001]. Each Fe 3+ ion is surrounded ( coordinated ) by six O 2- ions . The double layers are only weakly connected via H + ions, which is the reason for the complete cleavage parallel to the b-axis.

Modifications and varieties

The compound Fe 3+ O (OH) is trimorphic , so it occurs in addition to the orthorhombic crystallizing lepidocrocite as a trigonal crystallizing feroxyhyte and also as orthorhombic, albeit with a different space group and different cell parameters, crystallizing goethite .

A cryptocrystalline lepidocrocite became known under the outdated and discredited name glockerite in 1980 .

Education and Locations

Grainy lepidocrocite from the Siegerland - exhibited in the Mineralogical Museum Bonn

As a typical secondary mineral, lepidocrocite is formed by weathering or oxidation of other iron-containing minerals in the upper soil layers (e.g. as precipitation from the groundwater) as well as in mineral deposits or in marine manganese nodules . Together with goethite , lepidocrocite forms the main part of limonite ( brown iron stone ). In mineral deposits it is also grown on traubigem goethite or pyrite associated .

As a rather rare mineral formation, lepidocrocite can sometimes be abundant at various sites, but overall it is not very common. Around 400 sites are known worldwide (as of 2010). In Germany, in addition to its type locality in the Siegerland , the mineral is also found in the Black Forest , Odenwald , Fichtelgebirge , Upper Palatinate Forest , Spessart , Taunus , in the Harz , Sauerland , the Eifel , in the Hunsrück and in the Ore Mountains . In Austria, lepidocrocite was found mainly in the regions of Carinthia , Salzburg , Styria and Tyrol . In Switzerland, the mineral occurred mainly in the cantons of Bern , Schaffhausen , Wallis and Zurich .

Other locations are Egypt , Australia , Belgium , Bolivia , Brazil , Bulgaria , China , France , Greece , Greenland , India , Iran , Iran, Israel , Italy , Japan , Canada , Kazakhstan , Croatia , Madagascar , Mexico , Namibia , Netherlands , New Zealand , Norway , Poland , Portugal , Romania , Switzerland , Slovakia , Slovenia , Spain , South Africa , Czech Republic , Turkey , Ukraine , Hungary , Uzbekistan , the US Virgin Islands , the United Kingdom and the United States of America (USA). Lepidocrocite was also found in rock samples from the mid-Atlantic ridge .

use

Lepidocrocite is used as iron ore when it is locally accumulated .

See also

literature

Web links

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

Individual evidence

  1. ^ A b International Mineralogical Association: Commission on new Minerals and Mineral Names . In: International Mineralogical Association (Ed.): Mineralogical Magazine . tape  43 , 1980, pp. 1053-1055 ( rruff.info [PDF; 172 kB ; accessed on November 18, 2017]).
  2. ↑ a b c Johann Christoph Ullmann: IV. Metallic fossils. 256b. Iron mica. β. Pyrrhosiderite . In: Systematic and tabular overview of the mineralogically simple fossils: with explanatory notes . Kriegersche Buchhandlung, Cassel and Marburg 1814, p. 144 ( limited preview in Google Book search).
  3. ↑ Webmineral - Lepidocrocite (English)
  4. ↑ 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.  239 .
  5. ↑ a b c Lepidocrocite . 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; 69  kB ; accessed on November 18, 2017]).
  6. ↑ a b c d Lepidocrocite at mindat.org (English)
  7. ^ Johann Christoph Ullmann: IV. Metallic fossils. Notes . In: Systematic and tabular overview of the mineralogically simple fossils: with explanatory notes . Kriegersche Buchhandlung, Cassel and Marburg 1814, p. 316–317 ( limited preview in Google Book Search).
  8. ^ Johann Christoph Ullmann: IV. Metallic fossils. Notes . In: Systematic and tabular overview of the mineralogically simple fossils: with explanatory notes . Kriegersche Buchhandlung, Cassel and Marburg 1814, p. 299 ff . ( limited preview in Google Book search).
  9. ^ Johann Christoph Ullmann: IV. Metallic fossils. Notes . In: Systematic and tabular overview of the mineralogically simple fossils: with explanatory notes . Kriegersche Buchhandlung, Cassel and Marburg 1814, p. 451 ( limited preview in Google Book search).
  10. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  494-495 .
  11. ↑ Find location list for lepidocrocite at the Mineralienatlas and at Mindat