Akrochordite

Akrochordit is a very rarely occurring mineral from the mineral class of " phosphates, arsenates and vanadates ." It crystallizes in the monoclinic crystal system with the chemical composition (Mn, Mg) 5 [( OH) 2 | AsO4 ] 2 • 4H2O and usually develops spherical, wart-like ( hence the name ), but also prismatic crystals to about 2 mm in size or granular to massive mineral aggregates.

Etymology and history

Was first found Akrochordit 1922 in the Swedish mining community Långban and described by Gustav Flink (actually Gustaf Flink, 1849-1931 ), who named the mineral because of its characteristic wart-like crystal formation after the Greek word ἀκροχορδών [ Acrochordon ] for wart.

Classification

In the out-dated 8th edition of the mineral classification by Strunz the Akrochordit belongs to the department of " hydrous phosphates with foreign anions ", where he is the unnamed group VII/D.16 together with Chenevixite and Luetheit.

In force since 2001 9th edition of the Strunz'schen Mineral classification is the Akrochordit in the department of " phosphates with additional anions, with H2O" and the subsection "With only medium-sized cations, (OH, etc.): RO 4 = 2: 1 " sorted. There he forms as the eponymous mineral " Akrochorditgruppe " with the system no. 8.DD.10 with the other member Guanacoit.

The commonly used in English-speaking classification of minerals according to Dana assigns the Akrochordit in the department of " Hydrated Phosphates, etc., with hydroxyl or halogen " and then in the sub-division of " water -containing phosphates, etc., with hydroxyl or halogen with (AB ) 5 ( XO4 ) 2ZQ × x (H2O) ", where he also forms the unnamed group 42.04.01 along with Guanacoit.

Education and Locations

Akrochordit forms as a rare mineral in the hausmannite ore in a metamorphic formed iron-manganese ore body or in stratiform zinc deposits. Accompanying minerals include adjacent to Hausmannite still Pyrochroit, barite, Eveit, Brandtit, Sarkinit, Chlorophoenicit and various carbonates.

So far, only three localities for the Akrochordit known (as of 2010) are, in Sweden in addition to its type locality Långban nor the " Moss Mine" at Nordmark in the community Filipstad and in the U.S. the "Sterling Mine" at Sterling Hill in Ogdensburg, New Jersey.

Crystal structure

Akrochordit crystallizes isotypic with Guanacoit in the monoclinic crystal system, space group P21 / c with lattice parameters a = 8.68 Å; b = 17.63 Å; c = 6.83 Å and 99.5 ° β = and 2 formula units per unit cell.