Aldermanite

• IMA 1980-044

Aldermanit is a very rarely occurring mineral from the mineral class of " phosphates, arsenates and vanadates ." It crystallizes in the orthorhombic crystal system with the composition Mg5Al12 [( OH) 22 | ( PO4 ) 8] · 32H2O, is thus seen chemically a hydrous magnesium aluminum hydroxide as phosphate with additional anions.

Aldermanit found mostly in the form of fibrous or flaky mineral aggregates, which have a certain resemblance to Talk. Rarely, however, he also developed dünntafelige to prismatic, radialstrahlig arranged crystals of a few millimeters in size. In its pure form Aldermanit is colorless and transparent. But it can also appear white by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly.

Etymology and history

Aldermanit was first discovered in Moculta phosphate quarry near Angaston in the Barossa Valley of South Australia and described in 1981 by Ian R. Harrowfield, Edgar Ralph Segnit and John. A. Watts, who named the mineral after Arthur Richard Alderman ( 1901-1980 ).

Classification

Already in the now outdated but still in use 8th edition of the mineral classification by Strunz was one of Aldermanit to the mineral class of " phosphates, arsenates and vanadates " and then to the Department of " water -containing phosphates with foreign anions ", where he is the only member of the unnamed group VII/D.17 formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Aldermanit also in the class of " phosphates, arsenates and vanadates " and there in the department of " phosphates with additional anions, with H2O " one. This division, however, is further divided according to the relative size of the involved cations and the molar ratio of the other anions (OH, etc. ) to the phosphate, arsenate, or Vanadatkomplex ( RO 4 ), so that the mineral according to its composition in the subdivision " with only medium-sized cations, (OH, etc.): RO 4 = 3:1 "can be found where there is the unnamed group is the only member 8.DE.35.

The mainly common in English-speaking classification of minerals according to Dana assigns the Aldermanit in the class of " phosphates, arsenates and vanadates " and there in the department of " water -containing phosphates, etc., with hydroxyl or halogen" one. Here he is the only member of the unnamed group 42.13.01 within the sub-division of " water -containing phosphates, etc., with hydroxyl or halogen" to find.

Education and Locations

Aldermanit formed secondarily as a weathering product of fluellite in cavities of breccias in sedimentary phosphate deposits

Except at its type locality Moculta phosphate quarry, the mineral has been able (as of 2012) yet to be proven, in the resort also at Angaston Penrice marble quarry, as well as to Tom 's phosphate quarry near Kapunda in the Barossa Valley of South Australia.

Crystal structure

Aldermanit crystallized orthorhombic, with the exact space group has not been determined. The lattice parameters are a = 15.00 Å; b = 8.33 Å and c = 26.00 Å at 2 formula units per unit cell.