pyrrhotite


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Related to pyrrhotite: cinnabar, arsenopyrite, pentlandite, molybdenite

pyrrhotite

(pĭr`ətīt) or

magnetic pyrites,

bronze-yellow to bronze-red mineral, a sulfide of iron sometimes containing nickel. It tarnishes easily and is somewhat magnetic. It crystallizes in the hexagonal system, but appears usually in massive form, and occurs chiefly in basic igneous rocks. In some areas, e.g., at Sudbury, Ont., Canada, it is associated with pentlandite, an important ore of nickel. It is found also in the United States, Europe, and South America.

Pyrrhotite

 

(also pyrrhotine or magnetic pyrites), a sulfide mineral with composition Fe1-xS and containing admixtures of Ni and Co. Pyrrhotite’s crystal structure has hexagonal close packing of S atoms. It is defective, since not all the octahedral vacancies are occupied by Fe, as a result which certain Fe2+ are converted to Fe3+. The structural deficiency in Fe varies, and thus the compositions range from Fe0.875S (Fe7S8) to FeS (the stoichiometric composition FeS is known as troilite). The parameters and symmetry of the crystal cell vary according to the Fe deficiency and, when x ~ 0.11–0.2, pyrrhotite passes from the hexagonal modification to the monoclinic.

Pyrrhotite is brownish yellow with dark brown streaks and has a metallic luster. It usually occurs in the form of solid masses or granular deposits composed of intergrowths of both modifications. It has a hardness of 3.5–4.5 on Mohs’ scale and a density of 4,580–4,700 kg/m3. Its magnetic properties vary according to composition: hexagonal pyrrhotites, which are deficient in S, are paramagnetic, while monoclinic varieties, which are rich in S, are ferromagnetic. Some pyrrhotite minerals display distinctive magnetic anisotropy—paramagnetism in one direction and ferromagnetism in the other, perpendicular to the former.

Pyrrhotite is formed from hot solutions during a reduction in the concentration of dissociated S2– ions. It is widely distributed in hypogenic copper-nickel ore deposits associated with ultrabasic rocks, as well as in contact-metasomatic deposits and hydrothermal masses with copper-polymetallic, sulfide-cassiterite, and other types of mineralization. Pyrrhotite alters to pyrite, marcasite, and limonite in the zone of oxidation.

REFERENCE

Mineraly, vol. 1, Moscow, 1960.

G. P. BARSANOV

pyrrhotite

[′pir·ə‚tīt]
(mineralogy)
Fe1-x S A common reddish-brown to brownish-bronze mineral that occurs as rounded grains to large masses, more rarely as tabular pseudohexagonal crystals and rosettes; hardness is 4 on Mohs scale, and specific gravity is 4.6 (for the composition Fe7S8).
References in periodicals archive ?
Keywords: pyrrhotite bio-oxidation, kinetics, modelling, Monte Carlo simulation, parameter estimation
Minfile # 104J-024) and appears to be related to a fault that extends at least 3 km to Pyrrhotite Creek on the eastern flank of Mount Kaketsa.
Cormorant is a massive pyrrhotite breccia system that trends for approximately 5km both to the south and north of Cormorant.
0 metres depth containing strong stringer mineralization containing pyrite, pyrrhotite and trace chalcopyrite that graded 0.
Unit A-V: Pyrrhotite comprises 50-60% of sulfides and oxides, pyrite 10%-15%, scheelite 3%-5%, arsenopyrite 5%, Chalcopyrite 3%.
It is associated with pyrite and pyrrhotite mineralization and occurs in veins associated with quartz feldspar porphyries of the North Arm plutonic suite.
The KWG-Spider intersection inferred distal style VMS mineralization, the anomaly located 1200 meters to the NW on the new Freewest option property was interpreted as being proximal style mineralization, where higher copper values would be expected, however only pyrite and minor pyrrhotite was intersected in this hole, containing no significant copper or zinc values.
The KWG-Spider intersection inferred distal style VMS mineralization, the anomaly located 1,200 meters to the NW on the new Freewest option property was interpreted as being proximal style mineralization, where higher copper values would be expected, however only pyrite and minor pyrrhotite was intersected in this hole, containing no significant copper or zinc values.
In the high-grade zones discovered to date, gold occurs as free grains with pyrrhotite, chalcopyrite and pyrite.
Mineralization assemblages commonly contained pyrite with lesser pyrrhotite, with or without galena, sphalerite, chalcopyrite, and/or arsenopyrite.
Hole OPW-1, drilled at the southern end of this mineralized zone, and drilled at -69 degrees intersected pyrrhotite and chalcopyrite from 295m to 425m of core length.
Drillhole 05TB041 is the eastern-most hole and intersected two distinct zones of strongly silicified iron formation with up to 14% pyrrhotite and 6% pyrite.