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Jacobsite (Photo)

Synonym: Iwakiite is corrected to a tetragonal polytype Jacobsite-Q in 2018.

Year of discovery: 1869 (Jakobsberg mine, Sweden), 1954 (Japan)

Locality list: 119 localities of jacobsite

• MnFe₂O₄
• (Mn²⁺,Fe²⁺,Mg)(Fe³⁺,Mn³⁺)₂O₄
• [Mn²⁺][Fe³⁺₂][O₄]^8-

• Class: Spinel subgroup < Oxyspinel group < Spinel supergroup
• Class: Oxide
• Soluble in: HCl (with Cl₂ bubbles)
• Magnetism: Paramagnetic (Weak)

• Polymorph: Iwakiite (Tetragonal)

• Mn => Mg: Magnesioferrite
• Mn => Fe: Magnetite
• Mn => Zn: Franklinite
• Mn => Ni: Trevorite
• Mn => Cu: Cuprospinel
• Mn => Ge: Brunogeierite
• Mn => Ti: Ulvöspinel (Ulvospinel)

• Fe => Mn: Hausmannite
• Fe => V: Vuorelainenite
• Fe => Al: Galaxite
• Fe => Cr: Manganochromite

• Color: Black
• Streak: Brownish black
• Luster: Sub-Metallic
• Diaphaneity: Opaque

• Habit: Pyramidal or acicular elongated to [001]
• Twin: (-101)

• Cleavage: No
• Hardness: 5.5-6.5
• Density: 4.8

• System: Cubic (C), Tetragonal (Q) (Layer-stacking polytype)
• Group (C): m3m, Fd3m
• Group (Q): 4/mmm, I4₁/amd
• Lattice (C): a=8.5
• Lattice (Q): a=8.5, c=8.5

• Non-coexist: Quartz