Pyrrhotite

Formula: Fe_1-xS ( x = 0 to 0.17)

Origin of name: from Greek for redness

Crystal system: monoclinic

Crystal class: 2/m

Twinning: on {102}

Unit cell: a = 12.81 Å, b = 6.87 Å, c = 11.86 Å, b = 117.3°

Colour: bronze-yellow to bronze-red, tarnishes dark brown

Diaphaneity: opaque

Luster: metallic

Habit: crystals platy to tabular or bipyramidal, well-formed, massive, granular aggregates

Hardness: 3.5 to 4.5

Specific gravity: 4.53 to 4.77

Cleavage: 1; basal parting may be distinct

Tenacity: subconchoidal to uneven, brittle

Streak: grayish black

Synonyms/varieties:

Comments: data are for pyrrhotite-4C, there are also -5C, -6C, -7C and -11C polytypes and a high-temperature hexagonal polytype, which may remain stable at ordinary temperatures