A species of Pyrrhotite Group, Also known as Dipyrite (of Readwin), Kroeberite, Magnetic Iron Pyrites, Magnetopyrite, Pyrrohotite
Although pyrrhotite is a naturally occurring mineral used in concrete production, it can actually reverse the strength of concrete and cause it to crumble. Cement is mixed with pyrrhotite and solidifies into concrete; however, it starts to decompose when exposed to water and air. This process can crumble foundations and devastate homeowners. This mineral is common and is quite magnetic.
Hardness:
3.5 - 4
Density:
4.69 g/cm³
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Properties
Health Risk
Values
Characteristics
Cultural
Common Questions
General Info About Pyrrhotite
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Physical Properties of Pyrrhotite
Luster
Metallic
Diaphaneity
Opaque
Colors
Bronze brown, bronze red, dark brown
Magnetism
Magnetic
Tenacity
Brittle
Cleavage
None
Fracture
Subconchoidal
Streak
Dark grayish black
Crystal System
Monoclinic
Hardness
3.5 - 4 , Soft
Density
4.69 g/cm³, Obviously Heavy Weight
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Chemical Properties of Pyrrhotite
Chemical Classification
Sulfides
Formula
Fe1-xS
Elements listed
Fe, S
Common Impurities
Ni, Co, Cu
Health Risk of Pyrrhotite
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What is the hazards of Pyrrhotite?
Pyrrhotite has been linked to crumbling concrete basements in Quebec, Massachusetts and Connecticut when local quarries included it in their concrete mixtures. The iron sulfide it contains can react with oxygen and water over time to cause swelling and cracking.
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Rarity
Rare
Characteristics of Pyrrhotite
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Characteristics of Pyrrhotite
The ideal FeS lattice, such as that of troilite, is non-magnetic. Magnetic properties vary with Fe content. More Fe-rich, hexagonal pyrrhotites are antiferromagnetic. However, the Fe-deficient, monoclinic Fe7S8 is ferrimagnetic. The ferromagnetism which is widely observed in pyrrhotite is therefore attributed to the presence of relatively large concentrations of iron vacancies (up to 20%) in the crystal structure. Vacancies lower the crystal symmetry. Therefore, monoclinic forms of pyrrhotite are in general more defect-rich than the more symmetrical hexagonal forms, and thus are more magnetic. Monoclinic pyrrhotite undergoes a magnetic transition known as the Besnus transition at 30 K that leads to a loss of magnetic remanence. The saturation magnetization of pyrrhotite is 0.12 tesla.
Formation of Pyrrhotite
Pyrrhotite is a rather common trace constituent of mafic igneous rocks especially norites. It occurs as segregation deposits in layered intrusions associated with pentlandite, chalcopyrite and other sulfides. It is an important constituent of the Sudbury intrusion where it occurs in masses associated with copper and nickel mineralisation. It also occurs in pegmatites and in contact metamorphic zones. Pyrrhotite is often accompanied by pyrite, marcasite and magnetite. Pyrrhotite does not have specific applications. It is mined primarily because it is associated with pentlandite, sulfide mineral that can contain significant amounts of nickel and cobalt.
Composition of Pyrrhotite
Pyrrhotite exists as a number of polytypes of hexagonal or monoclinic crystal symmetry; several polytypes often occur within the same specimen. Their structure is based on the NiAs unit cell. As such, Fe occupies an octahedral site and the sulfide centers occupy trigonal prismatic sites. Materials with the NiAs structure often are non-stoichiometric because they lack up to 1/8th fraction of the metal ions, creating vacancies. One of such structures is pyrrhotite-4C (Fe7S8). Here "4" indicates that iron vacancies define a superlattice that is 4 times larger than the unit cell in the "C" direction. The C direction is conventionally chosen parallel to the main symmetry axis of the crystal; this direction usually corresponds to the largest lattice spacing. Other polytypes include: pyrrhotite-5C (Fe9S10), 6C (Fe11S12), 7C (Fe9S10) and 11C (Fe10S11). Every polytype can have monoclinic (M) or hexagonal (H) symmetry, and therefore some sources label them, for example, not as 6C, but 6H or 6M depending on the symmetry. The monoclinic forms are stable at temperatures below 254 °C, whereas the hexagonal forms are stable above that temperature. The exception is for those with high iron content, close to the troilite composition (47 to 50% atomic percent iron) which exhibit hexagonal symmetry.
Cultural Significance of Pyrrhotite
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Uses of Pyrrhotite
Pyrrhotite is currently used as a source of nickel, and has also historically been used as a source of iron and sulfur. Well-formed specimens are popular among collectors. It has been included in construction aggregates, but is implicated in the cracking of concrete and other such materials in more recent studies.
The History of Pyrrhotite
The name pyrrhotite is derived from Greek pyrrhos, flame-colored.
Etymology of Pyrrhotite
The name pyrrhotite is derived from Greek pyrrhos, flame-colored.
Common Questions People Also Ask
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