Simpsonite

Simpsonit is a rarely occurring mineral from the mineral class of oxides and hydroxides. It crystallizes in the trigonal crystal system with the chemical composition Al4 (Ta, Nb) 3O13 (OH ) and developed mostly euhedral to hypidiomorphe, tabular or short prismatic crystals in centimeter size that are either colorless or by foreign admixtures of yellow to brownish -yellow color.

Etymology and history

The first description of Simpsonit, as part of a tantalum- rich granite transferred (" Tabba Tabba pegmatite ") within the Pilbara Craton, comes from the Australian mineralogist H. Bowley. The type locality is situated about 50 km south of Port Hedland in the Australian state of Western Australia. Bowley named the mineral in honor of his colleague Edward Sydney Simpson (1875-1939), also a state-employed mineralogists, who contributed numerous scientific contributions to the mineralogy of Western Australia. The type material is now in the Western Australian Museum in Perth.

Classification

In the old ( 8th edition ) and new classification of minerals according to Strunz ( 9th edition ) of the Simpsonit belongs to the department of " oxides with the molar ratio of metal: oxygen = 1: 2 (and similar ) ". Since the 9th edition of the Strunz'schen system, however, this division is precisely divided by the size of the involved cations and the crystal structure, so that the mineral is now to be found in the subsection "With medium-sized cations and layers of edge-sharing octahedra ."

The classification of minerals according to Dana assigns the Simpsonit also to the class of oxides. There, however, he belongs to the department of " multiple oxides with niobium (Nb ), tantalum (Ta) and titanium ( Ti) ".

Education and Locations

Simpsonit rarely occurs as an accessory constituent in tantalum- rich granitic pegmatites. Accompanying minerals include beryl, microlite, muscovite, quartz, spodumene, tantalite and various tourmalines.

(As of 2009) So far, the mineral in 13 localities could be detected. In addition to the type locality in Australia, these include the Alto do Giz pegmatite in Ecuador / Borborema in Brazil; in the Tanco mine at Bernice Lake in Canada; in the Masisi Mountains of Kivu (Democratic Republic of Congo); East Kazakhstan ( Shyghys Qazaqstan ); Kola in Russia; and Mutoko and Bikita in Zimbabwe.

Crystal structure

Simpsonit trigonal crystallized in space group P3 with the lattice parameters a = 7.381 Å and c = 4.516 Å, and one formula unit per unit cell.