Lepidocrocite

• Ruby mica

Lepidocrocite (also ruby mica) is an abundant at several localities in part occurring, but overall little spread mineral from the group of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition of γ - Fe 3 O ( OH), and developed mostly tabular to short prismatic crystals to about 2 mm in size from dark red to red-brown color with reddish brown streak color, form the occasional rosette-shaped mineral aggregates. Also radialstrahlig -needle, granular, fibrous and earthy- massive aggregates are known. In the crystal faces is weak metal - to adamantine, fine aggregates, however, shows noble silky shine.

Etymology and history

Lepidocrocite was first discovered about the same time in the pit " Eisenzecher train " at Eiserfeld (Siegen ) in Germany and the Zlaté Hory ( German: Zuckmantel ) in the Czech Republic. The mineral was first described in 1813 by Johann Christoph Ullmann, who until acicular - fibrous crystal formation from the Greek words λεπιδιον it because of its occasionally foliated for " flaky " and κρόκη for " thread " or " tissue" named.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the lepidocrocite belonged to the mineral class of " oxides and hydroxides " and then to the Department of " hydroxides and oxide hydrates ," where he, along with akaganeite, boehmite, diaspore, Feitknechtit Feroxyhyt, goethite, Groutit, manganite, schwertmannite and Tsumgallit " akaganeite group " with the system no. IV/F.06 formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the lepidocrocite also in the class of " oxides and hydroxides ," there but in the fine already divided the department " hydroxides (excl. V or U) " a. This division is also further divided by the possible presence of hydroxide ions, and water of crystallization, and the crystal structure, so that the mineral according to its composition and structure in the sub-department " hydroxides with OH, excluding H2O; Layers of edge-sharing octahedra "can be found, where it forms the unnamed group 4.FE.15 only together with boehmite.

The classification of minerals according to Dana assigns the lepidocrocite in the class of " oxides and hydroxides " and there in the department of " hydroxides and hydroxy- oxides " one. Here he is with boehmite and Guyanait in the " Böhmitgruppe " with the system no. 06:01:02 within the subdivision " 06:01 hydroxides and hydroxy- oxides having the formula: X3 OOH " to find.

Modifications and varieties

The connection Fe3 O ( OH) trimorph, so come next to the orthorhombic crystallized lepidocrocite still as trigonal crystallizing Feroxyhyt and also as orthorhombic, albeit with a different space group and other cell parameters, crystallizing goethite before.

Education and Locations

Lepidocrocite forms as a typical secondary mineral weathering or oxidation of other iron-bearing minerals in the upper soil layers (eg as a precipitate from the groundwater ) as well as in mineral deposits or in marine manganese nodules. Together with goethite lepidocrocite forms the Hauptgemengteil of limonite ( limonite ). In ore deposits, he finds himself grew up on traubigem goethite or associated with pyrite.

Worldwide, lepidocrocite so far (as of 2010) are detected at around 400 localities. In Germany there is the mineral in addition to its type locality in the victor country in the Black Forest, Odenwald, Fichtelgebirge, Upper Palatinate Forest, Odenwald, Spessart, Taunus, in the Harz, Sauerland, the Eifel, the Hunsrück and in the Erzgebirge. In Austria lepidocrocite was found mainly in the regions Carinthia, Salzburg, Styria and Tyrol. In Switzerland, the mineral occurred mainly in the cantons of Bern, Schaffhausen, Valais and Zurich.

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

Crystal structure

Lepidocrocite crystallizes isotypic with boehmite in the orthorhombic crystal system, space group Cmc21 ( Raumgruppen-Nr. 36) with the lattice parameters a = 3.08 Å; b = 12.50 Å and c = 3.87 Å and four formula units per unit cell.

Use

Lepidocrocite is used in local accumulation as iron ore.