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Pyrrhotite

 
Pyrrhotite

 
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Pyrrhotite
 
 
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Pyrrhotite is an unusual iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 sulfide
Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
 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
Pyrite

The mineral pyrite, or iron pyrite, is an iron sulfide with the chemical formula ironsulfur2. This mineral's metallic Lustre and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold due to its resemblance to gold....
 because the color is similar to pyrite and it is weakly magnetic, the magnetism
Magnetism

In physics, magnetism is one of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic fiel...
 increases as the iron content decreases.

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.






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Pyrrhotite is an unusual iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 sulfide
Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
 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
Pyrite

The mineral pyrite, or iron pyrite, is an iron sulfide with the chemical formula ironsulfur2. This mineral's metallic Lustre and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold due to its resemblance to gold....
 because the color is similar to pyrite and it is weakly magnetic, the magnetism
Magnetism

In physics, magnetism is one of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic fiel...
 increases as the iron content decreases.

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
Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
 igneous rocks associated with pentlandite
Pentlandite

Pentlandite is an iron-nickel sulfide, 9sulfur8. Pentlandite usually has a Ni:Fe ratio of close to 1:1. It also contains minor cobalt....
, chalcopyrite
Chalcopyrite

Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2....
 and other sulfides. It also occurs in pegmatite
Pegmatite

Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic.Most pegmatites are composed of quartz, feldspar and mica; in essence a "granite"....
s and in contact metamorphic
Metamorphic rock

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form"....
 zones.

The troilite endmember, though only rarely encountered in the Earth's crust, is found in many meteorite
Meteorite

A meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. While in space it is called a meteoroid....
s. One iron meteorite, Mundrabilla, contains 25 to 35 volume percent troilite.