Roselite

• Roselit

• Ca2Co [ AsO4 ] 2.2 H2O
• Ca2 (Co, Mg) [ AsO4 ] 2.2 H2O

Roselite is a very rarely occurring mineral from the mineral class of " phosphates, arsenates and vanadates ." It crystallizes in the monoclinic crystal system with the idealized chemical composition Ca2Co [ AsO4 ] 2.2 H2O, is thus seen chemically a hydrous calcium -cobalt arsenate.

Roselite is the cobalt analogue of Wendwilsonit ( Ca2Mg [ AsO4 ] 2.2 H2O) and forms a complete solid solution series. In natural Roselite therefore is usually a small fraction of cobalt with magnesium replaced ( substituted ), which is expressed in the formula set out in parentheses element symbols: Ca 2 (Co, Mg) [ AsO4 ] 2.2 H2O

The mineral usually develops short prismatic crystals of a few millimeters to about one centimeter in length, but is also found in the form of Globular graphite or granular aggregates or embedded in Geodes and Druzes. The color of the transparent to translucent crystals varies depending on the cobalt content between light and dark pink to rose-red and the darker, the higher the cobalt content.

Special Features

Roselite is the Erythrin very similar in color, but can be distinguished from the latter by heating in a glass tube. Roselite itself changing in a characteristic way its color first in a strong glaze blue ( ultramarine ) and after quite cold in lavender blue. Erythrin (cobalt bloom ), however, assumes only a bluish black reputation.

Etymology and history

Was first described in 1824 by Armand Lévy Roselite who found the mineral on a piece from the collection of Charles Hampden Turner and named after the German mineralogist Gustav Rose. The chemical analysis led by John George Children, but was due to the small sample size does not determine the exact chemical composition.

A more detailed analysis of the mineral was achieved only by further discoveries 1873/74 in the mines of Schneeberg in Saxony's Ore Mountains, including the pits "Daniel" and " Rappold ". However, the latter yielded significantly cobalt -rich, dark rose -red crystals and therefore is generally regarded as the type locality for the Roselite.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Roselite belonged to the department of " water -containing phosphates without foreign anions ", where he. Together with Fairfieldit the " Fairfieldit - Roselite group " with the system no Formed VII/C.17 and the other members Brandtit, Cassidyit, Roselite - β, Collinsit, Gaitit, Hillit, Messelit, Parabrandtit, Talmessit, Wendwilsonit and Zinkroselith.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Roselite also in the department of " Phosphates without additional anions, with H2O" one. However, this is further divided according to the relative size of the involved cations and the molar ratio of phosphate, arsenate or Vanadatkomplex ( RO 4 ) to water of crystallization, so that the mineral according to its composition in the subsection "With large and medium-sized cations, RO 4: H 2 O = 1, " is to find where it only together with Brandtit, Wendwilsonit and Zinkroselith the" 1 Roselithgruppe "with the system no. 8.CG.10 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the Roselite in the class of " phosphates, arsenates and vanadates " and there in the department of " water containing phosphates, etc. " field. Here he is as the namesake of the " Roselite subgroup ( Monoclinic: P21 / c) " with the system no. 40.02.03 and the other members Brandtit, Manganlotharmeyerit, Wendwilsonit and Zinkroselith within the subdivision " water containing phosphates, etc., with A2 ( B2 ) 2 ( XO4 ) × x (H2O) " to find.

Education and Locations

Roselite formed secondarily in cobalt-containing, hydrothermal deposits. As an accessory mineral occurs among other Talmessit.

A rare mineral formation Roselite could be detected only in a few localities, where so far (as of 2013) are about 20 localities known as. Apart from its type locality " pit Rappold " entered the mineral nor in other mines of the Marx -Semler - adit system to Neustädtel in a circle Schneeberg in Saxony, the pits " Friedrich- Christian " in Wildschapbachtal and " St. Anton " in Heubachtal in Baden -Württemberg, at home and in the circle Mack Richelsdorf in Hessen and in the pit " Green Off " at Schutzenbach in Rhineland -Palatinate on.

A well-known locality for Roselite are the deposits at Bou Azzer ( Bou Azer ) near Tazenakht in the Moroccan province of Ouarzazate, where in the last 80 days and sub- surface mines rich cobalt, silver and nickel ores are mined and also many beautiful Roselite levels were revealed. As in Bou Azzer however, the color similar minerals Erythrin and Wendwilsonit occur, the likelihood of confusion is high, especially Wendwilsonit is purely visually almost indistinguishable due to its chemical similarity as a solid solution partner from Roselite.

Other localities lie among other things, " Veta Negra mine " in the Pampa Larga District ( Tierra Amarilla ) in the Chilean province of Copiapo, the " Talmessi Mine" at Anarak in the Iranian province of Esfahan and the " Silvana Mine" at Sandon in the Canadian province of British Columbia.

Crystal structure

Roselite crystallizes isotypic with Fairfieldit in the monoclinic crystal system, space group P21 / c ( Raumgruppen-Nr. 14) with the lattice parameters a = 5.80 Å; b = 12.90 Å; c = 5.62 Å and 107.4 ° and β = 2 formula units per unit cell.