janggunite

{{infobox mineral | name = Janggunite | image = Janggunite-purplesky.jpg | alt = | caption = Janggunite found in South Korea | category = Oxide mineral | formula = {{chem2|Mn_{5−x}(Mn,Fe)_{1+x}O8(OH)6}} | IMAsymbol = Jgn | strunz = 4.FG.05 | dana = | system = Orthorhombic | symmetry = Pman | unit cell = a = 9.324, b =14.05 c = 7.956 [Å], Z = 4 | molweight = | color = Black | colour = | habit = | twinning = | cleavage = Perfect, one direction | fracture = | tenacity = Fragile | mohs = 2 - 3 | luster = Dull | streak = Brownish black to dark brown | diaphaneity = | gravity = 3.59 | density = | polish = | opticalprop = Biaxial | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = }} Janggunite is a rare manganese oxide mineral with the chemical formula {{chem2|Mn_{5−x}(Mn,Fe)_{1+x}O8(OH)6}}.

It was first described in 1975 for an occurrence in the Janggun mine, Bonghwa-gun, Gyeongsangbuk-do, South Korea and named for the locality.