Images
Formula: Na(Mn4+7Mn3+)O16
Multiple oxide, coronadite group,
hollandite supergroup,
manganese-bearing mineral
Crystal System: Tetragonal
Specific gravity: 4.29 measured, 4.23 calculated
Hardness: 3 to 3½
Streak: Brownish black
Colour: Dark brownish grey
Luminescence: Not fluorescent under UV
Environments
Manjiroite is found in the oxidation zone of metamorphosed bedded
manganese
deposits, associated with romanèchite and
todorokite
(Mindat).
Localities
At the Pilbara manganese belt, Western Australia, manjiroite is associated with
cryptomelane, pyrolusite,
nsutite and romanèchite
(HOM).
At the type locality, the Kohare mine, Karumai, Iwate Prefecture, Japan, manjiroite occurs in the oxidation zone
of rhodonite-tephroite-rhodochrosite
bedded ore deposits, in dense compact black masses up to 10 x 8 x 5 cm3. Associated minerals include
pyrolusite, nsutite,
birnessite, cryptomelane and
goethite, as well as tephroite,
rhodonite and rhodochrosite
(AM 53.2103-2106, Mindat).
At the Smartt Mine, Kalahari manganese field, Northern Cape, South Africa, Asbestiform manjiroite and
todorokite occur as infill of bedding parallel extension veinlets in
supergene altered
braunite-kutnohorite
mudstone
(South African Journal of Geology 103.163–174).
Back to Minerals