Shigaite

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title: "Shigaite" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["sulfate-minerals", "manganese(ii)-minerals", "aluminium-minerals", "trigonal-minerals", "minerals-in-space-group-148"] description: "Mineral" topic_path: "general/sulfate-minerals" source: "https://en.wikipedia.org/wiki/Shigaite" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Mineral ::

::data[format=table title="Infobox mineral"]

Field	Value
name	Shigaite
category	Sulfate mineral
image	Rhodochrosite-Shigaite-cktsr-4a.jpg
caption	Reddish-brown shigaite crystal (2 cm across) with pink rhodochrosite from South Africa
formula	NaAl3(Mn2+)6(SO4)2(OH)18·12H2O
IMAsymbol	Sga
strunz	7.DD.35
dana	31.1.2.1
system	Trigonal
class	Rhombohedral ()
H-M symbol: ()
symmetry	R
unit cell	a = 9.51 Å, c = 32.83 Å, Z = 3
color	Yellow, burnt orange, brown, black
twinning	On {0001}
cleavage	Perfect on {0001}
tenacity	Moderately flexible
mohs	2
luster	Vitreous to dull
refractive	n = 1.546
opticalprop	Uniaxial (−)
pleochroism	Distinct; O = yellow; E = very pale yellow
fluorescence	Non-fluorescent
streak	Very pale yellow to white
gravity	2.32
diaphaneity	Transparent
::

| name = Shigaite | category = Sulfate mineral | boxwidth = | boxbgcolor = | image = Rhodochrosite-Shigaite-cktsr-4a.jpg | imagesize = | caption = Reddish-brown shigaite crystal (2 cm across) with pink rhodochrosite from South Africa | formula = NaAl3(Mn2+)6(SO4)2(OH)18·12H2O | IMAsymbol = Sga | molweight = | strunz = 7.DD.35 | dana = 31.1.2.1 | system = Trigonal | class = Rhombohedral () H-M symbol: () | symmetry = R | unit cell = a = 9.51 Å, c = 32.83 Å, Z = 3 | color = Yellow, burnt orange, brown, black | habit = | twinning = On {0001} | cleavage = Perfect on {0001} | fracture = | tenacity = Moderately flexible | mohs = 2 | luster = Vitreous to dull | polish = | refractive = n = 1.546 | opticalprop = Uniaxial (−) | birefringence = | 2V = | dispersion = | pleochroism = Distinct; O = yellow; E = very pale yellow | fluorescence= Non-fluorescent | absorption = | streak = Very pale yellow to white | gravity = 2.32 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent | other = | references = Shigaite is a mineral with formula NaAl3(Mn2+)6(SO4)2(OH)18·12H2O that typically occurs as small, hexagonal crystals or thin coatings. It is named for Shiga Prefecture, Japan, where it was discovered in 1985. The formula was significantly revised in 1996, identifying sodium as a previously unknown constituent.

Description

::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/e5/Shigaite-Rhodochrosite-201388.jpg" caption="Dark-red and yellow shigaite on pink rhodochrosite"] ::

Shigaite occurs as hexagonal tabular crystals up to 2 cm in size or as thin films and coatings. The mineral can be yellow, burnt orange, brown or black in color.

Structure

Shigaite consists of oxycation sheets of [AlMn2+2(OH)6]1+ intercalated with oxyanion sheets of [Na(H2O)6{H2O}6(SO4)2]3−. Linkage between the sheets and within the oxyanion sheet results largely through hydrogen bonding.

History

Shigaite was discovered in 1985 in the Ioi Mine, Shiga Prefecture, Japan. Sodium, discovered to be a component of shigaite, was not identified in the original study. However, an unidentified volatile had been noted that presumably was a sodium-containing complex.

Distribution

, shigaite is known from the following sites:

• Iron Monarch open cut, South Australia, Australia
• Poudrette quarry, Quebec, Canada
• Ioi mine, Shiga Prefecture, Japan
• Wessels Mine, Northern Cape Province, South Africa
• N'Chwaning Mine, Northern Cape Province, South Africa
• Homer Mine, Michigan, United States
• Bengal Mine, Michigan, United States

The type material is housed in the National Museum of Natural History in Washington, D.C. as sample 122089.

Association

Shigaite has been found associated with the following minerals: Ioi mine, Japan

• rhodochrosite
• sonolite
• manganosite
• pyrochroite
• jacobsite
• hausmannite
• galaxite

Wessels Mine, South Africa

• rhodochrosite
• leucophoenicite
• gageite
• caryopilite

Iron Monarch, South Australia

• arsenoclasite
• gatehouseite
• hematite
• hausmannite
• manganoan ferroan calcite
• barite
• gypsum

Notes

References

Bibliography

References

1. Nickel, Ernest H.. "IMA/CNMNC List of Mineral Names". Materials Data, Inc..
2. Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
3. "Shigaite". Mindat.
4. "Shigaite". Mineral Data Publishing.
5. "Shigaite Mineral Data". Webmineral.
6. Shigaite occurs in [[metamorphosed]] deposits of [[manganese ore]] and is the [[manganese|Mn²⁺]] analogue of [[motukoreaite]].Cooper, p. 91.
7. (November–December 1986). "New Mineral Names". American Mineralogist.
8. The original study, published in the journal ''Neues Jahrbuch für Mineralogie, Monatshefte'', identified the formula as Al₄Mn₇(SO₄)₂(OH)₂₂·8H₂O. The formula was significantly revised in 1996 using a sample from the N'Chwaning Mine, South Africa.Cooper, p. 91.
9. Cooper, p. 96.

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