Formula: Mn6Al3(OH)18[Na(H2O)6](SO4)2.6H2O
Hydrated sulphate containing hydroxyl, manganese-bearing mineral
Crystal System: Trigonal
Specific gravity: 2.32 measured, 2.35 calculated
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).
Back to Minerals