Summary: Janggunite occurs as radiating groups of flakes, flower-like aggregates, colloform bands, dendritic or arborescenl masses in the cementation zone of the supergene manganese oxide deposits. The flakes average 0·05 mm. Colour black, lustre dull, streak brownish black to dark brown. Cleavage one direction perfect. H = 23, very fragile. Dmeas = 3·59, Dcalc = 3·58. Under reflected light anisotropic and bireflectant. No internal reflections. Etching reactions: positive - HC1, HNO3, SnCl2, H2O2, H2SO4 + H2O2. Chemical formula, Mn4·854+( Mn0·902+ Fe0·303+)O8·09(OH)5·91 on the basis of O = 14, or ideally Mn5−x4+(Mn2++Fe3++)1+xO8(OH)6(x=0·2). The mineral has an orthorhombic unit cell with a 9·324, b 14·05, c 7·956 Å, Z = 4, a:b:c = 0·663:1:0·566. Important diffraction lines are 9·34(s), 7·09(s), 4·62(m), 4·17(m), 3·547(s), 3·101(s), 2·597(w), 2·469(m), 1·863(w), 1·664(w), 1·525(m), 1·405(m), D.T.A. curve shows the endothermic peaks at 250–370°C and 955°C Infra-red absorption spectral curve shows vibrations at 515 cm−1, 545 cm−1, 1025 cm−1, and 3225 cm−1. The mineral and name have been approved before publication by the Commission on New Minerals and Mineral Names, I.M.A.