Janggunite

Janggunite is a rare manganese oxide mineral with the chemical formula Mn_5−x(Mn,Fe)_1+xO₈(OH)₆.

Janggunite
Janggunite found in South Korea
General
Category	Oxide mineral
Formula	Mn5−x(Mn,Fe)1+xO8(OH)6
IMA symbol	Jgn[1]
Strunz classification	4.FG.05
Crystal system	Orthorhombic
Space group	Pman
Unit cell	a = 9.324, b =14.05 c = 7.956 [Å], Z = 4
Identification
Color	Black
Cleavage	Perfect, one direction
Tenacity	Fragile
Mohs scale hardness	2 - 3
Luster	Dull
Streak	Brownish black to dark brown
Specific gravity	3.59
Optical properties	Biaxial
References	[2][3][4]

It was first described in 1975 for an occurrence in the Janggun mine, Bonghwa-gun, Gyeongsangbuk-do, South Korea and named for the locality.^[3]