shigaite

{{Infobox mineral | 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== thumb|left|Dark-red and yellow shigaite on pink rhodochrosite Shigaite occurs as hexagonal tabular crystals up to in size or as thin films and coatings. The mineral can be yellow, burnt orange, brown or black in color. Shigaite occurs in metamorphosed deposits of manganese ore and is the Mn2+ analogue of motukoreaite.