Troilite

Troilite ( iron pyrites, Meteor gravel) is a rare, because almost exclusively in meteorites occurring mineral from the mineral class of sulfides ( and sulfosalts ). It crystallizes in the hexagonal crystal system with the chemical composition FeS and developed in iron meteorites microcrystalline, massive aggregates of metallic luster, gray -brown to bronze- brown color.

Etymology and history

Troilite was discovered very early on as a striking, bright shiny mineral in meteorites and called iron pyrites or Meteor gravel. It was named after the Italian finally Father Dominico Troili, who described him in 1766 as one of the first. He found a shiny yellow mineral in the olivine - hypersthene chondrite that fell in Albareto ( Modena, Italy).

Special Features

In contrast to terrestrial pyrrhotite chemical analysis always results when Troilite the atomic ratio of 50% iron (Fe ) and 50% sulfur (S ) (where small amounts are added to cobalt and nickel iron ). When pyrrhotite always a deficiency of iron in the formula shows ( about 48 to 49 atomic % Fe). The reason for this is that the meteoritic troilite always with metallic iron is in equilibrium, the earthly pyrrhotite ( Fe7S8 ) is not.

Modifications and varieties

Troilite the high-temperature modification of the iron sulfide and only above about 300 ° C is stable.

Classification

In the old ( 8th edition ) and new classification of minerals ( 9th Edition ) by Strunz and after the mineral classification by Dana is the troilite to mineral class of sulfides with the molar ratio of metal: sulfur ( selenium, tellurium ) = 1: 1

Education and Locations

Troilite comes as Nebengemengteil in almost all meteorite types and occurs mostly on there in paragenesis with taenite and kamacite. Chondrites, the most common meteorite class, containing about 5% troilite in the form of small (up to about 1 mm) irregular grains. In iron meteorite troilite occurs in cm - large inclusions, often with graphite. Also achondrites contain troilite than small grains.

The mineral was found among others in the following meteorites and their impact craters: HOW 88403 ( Ataxit meteorite ), LAP 02205 ( lunar meteorite ), ALH 77283 and ALH 84008 ( Allan Hills Icefield, Victoria Land ) in Antarctica; Campo del Cielo, Pampa del Infierno and El Sampal in Argentina; Henbury, Tenham, Little Minnie Creek and North Haig in Australia; Quijingue and Ibitira in Brazil; Benton and Saint -Robert meteorite in Canada; Neuschwanstein and Ramsdorf in Germany; Albareto, Barbianello, Fermo, Lake Valscura and Malenco in Italy; Witwatersrand in South Africa; Tataouine in Tunisia.

Crystal structure

Troilite crystallized in the hexagonal crystal system in space group P63/mmc with lattice parameters a = 3.452 Å and c = 5.762 Å and two formula units per unit cell.