Strengite

Strengit is a rarely occurring mineral from the mineral class of " phosphates, arsenates and vanadates ." It crystallizes in the orthorhombic crystal system with the composition Fe 3 [ PO4 ] · 2H2O, is thus seen chemically a hydrous iron (III ) phosphate.

Strengit forms from different crystal forms, but which dominate octahedral and stretched according to the c-axis, ridge-like shapes. These can be several centimeters long and show on the surfaces of a glass-like shine. In addition there are also fibrous, grape-like and spherical mineral aggregates.

In its pure form Strengit is colorless and transparent. But it can also appear white and accept by foreign admixtures a pink to violet, peach blossoms - to carmine or greenish white color by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly. His stroke color, however, is always white.

With variscite (Al [ PO4 ] · 2H2O) Strengit forms a complete solid solution series.

Etymology and history

Was first discovered in the pit Strengit Eleonore near Giessen in the Beaver (Hessen) and described in 1877 by August Nies, who named the mineral after his teacher and professor of mineralogy Johann August Stern ( 1830-1897 ).

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Strengit belonged to the department of " water -containing phosphates without foreign anions ", where he along with Kolbeckit, Koninckite, Mahlmoodit, Mansfieldit, metavariscite, Paraskorodit, Phosphosiderit, scorodite, Variscite and Yanomamit the " Variscit group " with the system no. VII/C.09 formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Strengit 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 vanadate complex ( RO 4 ) to the contained water of crystallization, so that the mineral according to its composition in the subsection "With only medium-sized cations, RO 4: H2O = 1: " is to find where it only together with Mansfieldit, Redondit, scorodite, Variscite and Yanomamit the " 2 Variscit group "with the system no. 8.CD.10 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the Strengit in the class of " phosphates, arsenates and vanadates " and there in the department of " water containing phosphates, etc. " field. He is also, along with Variscite, scorodite, Mansfieldit and Yanomamit in the " Variscit group " with the system no. 40.04.01 found within the sub-division of " water -containing phosphates, etc., with A3 XO4 × x (H2O) ".

Modifications and varieties

The connection Fe3 [ PO4 ] · 2H2O is dimorphic and comes in addition to the orthorhombic modification Strengit before crystallizing as monoclinic Phosphosiderit.

As Vilateit a manganese-containing variety of Strengit is called.

Education and Locations

Strengit forms in phosphate-containing, granitic pegmatites or secondarily by hydrothermal replacement of primary phosphate minerals. Accompanying minerals occur among others apatite, Beraunite, Bermanit, Dufrénit, Hureaulith, Cacoxenite, Leukophosphit, Phosphosiderit, Rockbridgeite, stewartite and vivianite.

As a rather rare mineral formation Strengit can indeed be abundant in part to different sites, overall it is not very common. So far (as of 2013) are considered to be known around 240 localities. Apart from its type locality Eleonore mine and the nearby Dünsberg around pouring the mineral still occurred in Germany in the Clara mine in Baden- Württemberg; in several places around Hagendorf ( Waidhaus ) and other places in the Upper Palatinate Forest and Auerbach in der Oberpfalz and the chicken Kobel in Bavaria; at Görzklinge / Kirschhausen, the pit Jacob blessing in Bremthal, the Rotläufchen Mine in Waldgirmes and Essershausen in Hesse; at several points in the Fund Sauer and winners district of North Rhine -Westphalia; at Rengersdorf and Hartmannsgrün / Oelsnitz / Vogtl. in Saxony as well as in Ullersreuth in Thuringia.

In Austria Strengit could previously only be found in Ganztal in the Fischbacher Alps and at Duke mountain near Modriach in Styria.

Known due to exceptional Strengitfunde among others, the " Bull Moose Mine" is at Custer in the U.S. state of South Dakota, where violet crystals of up to five millimeters in size were revealed.

Other localities lie among others in Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, Finland, France, French Guyana, Iran, Italy, Japan, Cameroon, Canada, Liberia, Madagascar, Malaysia, Mali, Mexico, Morocco, Namibia, Portugal, Rwanda, Romania, Russia, Sweden, Senegal, Spain, South Africa, South Korea, Czech Republic, Uruguay, the United Kingdom ( UK) and the United States of America (USA).

Crystal structure

Strengit crystallizes in the orthorhombic space group PCAB ( Raumgruppen-Nr. 61) with the lattice parameters a = 10.12 Å; b = 9.89 Å and c = 8.72 Å, and eight formula units per unit cell.