Stillwaterite

• IMA 1974-029

Stillwaterit is a very rarely occurring mineral from the mineral class of sulfides and sulfosalts. It crystallizes in the hexagonal crystal system with the chemical composition and forms Pd8As3 anhedrale grains of size of up to 265 microns creamy gray color.

Etymology and history

The mineral was in 1975 by L. J. Cabri, J.L.G. Laflamme, J. M. Stewart, J. F. Discovered Rowland and Tzong R. Chenin in the type locality, the Stillwater Complex, a rock formation in the U.S. state of Montana. It is also named after this.

Classification

In the classification by Strunz Stillwaterit is counted among the alloys and alloy- like compounds, a subset of the sulfides and sulfosalts. After the 8th edition forms a group together with Arsenopalladinit, Atheneit, Genkinit, Itoigawait, Majakit, Menshikovit, Mertieit -I, Mertieit -II, Palladoarsenid, Palladobismutoarsenid, Palladodymit, Polkanovit, Rhodarsenid, Stibiopalladinit, Ungavait and Vincentit. In the 9th edition it forms with Arsenopalladinit, Mertieit -II and Palarstanid a subset of compounds of semi-metals with platinum - group elements (PGE ).

In the classification by Dana, it forms a separate subgroup of the sulfides, selenides and tellurides with different formulas.

Education and Locations

Stillwaterit forms in layered ultramafic igneous rocks. It is associated with gold, Palladoarsenid, Sperrylit, Braggit, Hollingworthit, chalcopyrite, digenite, pentlandite and pyrrhotite.

From the very rare mineral only a few localities are known. In addition to the type locality was found Stillwaterit in Lapland (Finland), Porsanger in Norway, the Russian Murmansk Oblast, and in the Bushveld complex in South Africa.

Crystal structure

Stillwaterit crystallizes in the hexagonal crystal system in space group P3 or with the lattice parameters a = 7.392 to 7.399 Å and c = 10.311 Å and three formula units per unit cell.