Pyrrhotite

Pyrrhotite
Brassy, tabular crystals of pyrrhotite, with sphalerite and quartz, from Nikolaevskiy Mine, Primorskiy Kray, Russia. Specimen size: 5.3 × 4.1 × 3.8 cm
General
Category	Mineral
Formula (repeating unit)	Fe1−xS (x = 0 to 0.125)
IMA symbol	Pyh[1]
Strunz classification	2.CC.10
Crystal system	Monoclinic, with hexagonal polytypes
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	A2/a
Unit cell	a = 11.88 Å, b = 6.87 Å, c = 22.79 Å; β = 90.47°; Z = 26
Identification
Color	Bronze, dark brown
Crystal habit	Tabular or prismatic in hexagonal prisms; massive to granular
Cleavage	Absent
Fracture	Uneven
Mohs scale hardness	3.5 – 4.5
Luster	Metallic
Streak	Dark grey – black
Specific gravity	4.58 – 4.65, average = 4.61
Refractive index	Opaque
Fusibility	3
Solubility	Soluble in hydrochloric acid
Other characteristics	Weakly magnetic, strongly magnetic on heating; non-luminescent, non-radioactive
References	[2][3][4]

Pyrrhotite (pyrrhos in Greek meaning "flame-coloured") is an iron sulfide mineral with the formula Fe_(1-x)S (x = 0 to 0.125). It is a nonstoichiometric variant of FeS, the mineral known as troilite. Pyrrhotite is also called magnetic pyrite, because the color is similar to pyrite and it is weakly magnetic. The magnetism decreases as the iron content increases, and troilite is non-magnetic.^[5] Pyrrhotite is generally tabular and brassy/bronze in color with a metallic luster. The mineral occurs with mafic igneous rocks like norites, and may form from pyrite during metamorphic processes.^[6] Pyrrhotite is associated and mined with other sulfide minerals like pentlandite, pyrite, chalcopyrite, and magnetite, and has been found globally.