Shigaite

shigaite

arsenoclasite

manganosite

gatehouseite

Formula: Mn6Al3(OH)18[Na(H2O)6](SO4)2.6H2O

Hydrated sulphate containing hydroxyl
Specific gravity: 2.32
Hardness: 2
Streak: Yellow-white
Colour: Deep yellow with black, inhomogenous inclusions
Environments:

Metamorphic environments
Hydrothermal environments

Shigaite is a rare secondary mineral in metamorphosed manganese ore deposits (HOM).

Localities

At the Iron Monarch open cut, Iron Knob, Middleback Range, Eyre Peninsula, South Australia, shigaite is associated with arsenoclasite, gatehouseite, hematite, hausmannite, manganoan ferroan calcite, baryte and gypsum. It is closely associated with a baryte-rich zone, and the specimens from the Kalahari manganese field are frequently associated with baryte as well (HOM, R&M 91.2.150-153).

At the type locality, the Ioi mine, Ritto City, Shiga Prefecture, Japan, shigaite occurs as a secondary phase in veins cutting altered manganosite - rhodochrosite - sonolite ore. Associated minerals include pyrochroite, jacobsite, hausmannite and galaxite (AM 71.1546, Dana), as well as rhodochrosite, sonolite and manganosite (HOM, R&M 91.2.150-153).

At the Wessels mine, Hotazel, Kalahari manganese field, Northern Cape, South Africa, shigaite is associated with rhodochrosite, leucophoenicite, gageite and caryopilite (HOM).

At the N'Chwaning I Mine, Kuruman, Kalahari manganese field, Northern Cape, South Africa, shigaite is associated with baryte, kutnohorite, manganese-bearing calcite, pyrochroite, rhodochrosite and fibrous sussexite, although much of the sussexite was subsequently washed off the specimens. The most common associated mineral was drusy pink rhodochrosite that frequently lined the cavities and formed the matrix for the shigaite crystals (R&M 91.2.150-153).

At the Cannon mine (Bengal-Tully mine), Stambaugh, Iron county, Michigan, USA, Bengal mine Michigan, shigaite has been found associated with seamanite, hematite and rhodochrosite (R&M 91.2.150-153).

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