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Pyrrhotite



Pyrrhotite

General
CategoryMineral
Chemical formulairon sulfide:Fe1-xS (x = 0 to 0.2)
Identification
ColorBronze
Crystal habitTabular or prismatic in hexagonal prisms; massive to granular
Crystal systemhexagonal, 6/m2/m2/m and monoclinic, 2/m
CleavageAbsent
FractureUneven
Mohs Scale hardness3.5 - 4.5
LusterMetallic
Refractive indexOpaque
StreakDark grey - black
Specific gravity4.6
Fusibility3
SolubilitySoluble in hydrochloric acid
Other CharacteristicsWeakly magnetic, strongly magnetic on heating

Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: Fe(1-x)S (x = 0 to 0.2). The FeS endmember is known as troilite. Also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic, the magnetism increases as the iron content decreases.

Additional recommended knowledge

Pyrrhotite is odd also because it has two crystal symmetries. When pyrrhotite is high in iron and the formula is closer to true FeS the structure is hexagonal. But, when it is low in iron, the structure is monoclinic. Both symmetries occur together in the same specimen.

The name is derived from Greek pyrrhos, flame-colored.

Pyrrhotite is a rather common trace constituent of igneous rocks. It occurs as segregation deposits from mafic igneous rocks associated with pentlandite, chalcopyrite and other sulfides. It also occurs in pegmatites and in contact metamorphic zones.

The troilite endmember, though only rarely encountered in the Earth's crust, is found in many meteorites. One iron meteorite, Mundrabilla, contains 25 to 35 volume percent troilite.[1]

References and external links

  • Dana's Manual of Mineralogy ISBN 0-471-03288-3
  • Mineral Galleries: Pyrrhotite
  • Webmineral.com
  • Mindat.org
  1. ^ Vagn Buchwald, Handbook of Iron Meteorites, 1975.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Pyrrhotite". A list of authors is available in Wikipedia.
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