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Formula: Mn2+(SO4).5H2O
Hydrated manganese sulphate,
chalcanthite group
Crystal system: Triclinic
Specific gravity: 2.03 measured, 2.094 calculated
Hardness: 2½
Streak: White
Colour: Pale pink
Solubility: Readily soluble in water
Environments
Jôkokuite dehydrates to ilesite at 20oC and 50% humidity.
Localities
At the type locality, the Johkoku mine, Kaminokuni, Hiyama District, Hiyama Subprefecture, Hokkaidō Prefecture,
Japan, jôkokuite occurs as stalactites, up to about 5 cm long and 1 cm across, composed of irregular and
fine-grained crystals with a mozaic texture. Individual grains are less than 0.05 mm across; it also occurs as
efflorescences in oxidised portions of mine workings, apparently deposited from mine waters at 25oC.
Associated minerals include gypsum,
szmikite, ilesite,
rozenite, siderotil,
ferrohexahydrite,
mallardite, melanterite
and goslarite. The ores at the mine consist mainly of
rhodochrosite with lesser amounts of
sphalerite, galena,
pyrite, marcasite and others.
(AM 64.652-659, Mindat, HOM).
Jôkokuite from the Johkoku Mine -
IMage
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