Pyrophanite

(repeating unit)MnTiO₃IMA symbolPph^[1]Strunz classification4.CB.05Dana classification4.3.5.3Crystal systemTrigonalCrystal classRhombohedral (3)
(same H-M symbol)Space groupR3Unit cella = 5.13948(7) Å,
c = 14.2829(4) Å; Z = 6IdentificationColorDeep blood-red to greenish blackCrystal habitRarely as rosettes of hexagonal plates, typically granular, scaly; occurs as exsolution lamenae in franklinite and spinelCleavagePerfect on {0221}FractureConchoidalTenacityBrittleMohs scale hardness5–6LusterSubmetallicStreakOchre yellowDiaphaneitySubtranslucent to opaqueSpecific gravity4.537 measuredOptical propertiesUniaxial (-)Refractive indexn_ω = 2.481 n_ε = 2.210Birefringenceδ = 0.271Common impuritiesFe, ZnReferences^[2][3][4]

Pyrophanite is a manganese titanium oxide mineral with formula: MnTiO₃. It is a member of the ilmenite group. It is a deep red to greenish black mineral which crystallizes in the trigonal system.

Discovery and occurrence

It was first described in 1890 from an occurrence in the Harstigen Mine, Filipstad, Värmland, Sweden.^[3] Its name was derived from the Greek πΰρ, fire, and φαίνεσθαι, to appear, because of the deep red color of the mineral.^[3]

Its main occurrence is in manganese deposits that have undergone metamorphism. It also occurs in granite, amphibolite and serpentinite as an uncommon accessory mineral. Associated minerals include ilmenite, geikielite, hematite, spinel, gahnite, chromite, magnetite, ganophyllite, manganophyllite, hendricksite, garnet and calcite.^[2]

References