Shigaite information

Shigaite
Shigaite
	Reddish-brown shigaite crystal (2 cm across) with pink rhodochrosite from South Africa
General
Category	Sulfate mineral
Formula; (repeating unit)	NaAl3(Mn2+)6(SO4)2(OH)18·12H2O
IMA symbol	Sga
Strunz classification	7.DD.35
Dana classification	31.1.2.1
Crystal system	Trigonal
Crystal class	Rhombohedral (3) ; H-M symbol: (3)
Space group	R3
Unit cell	a = 9.51 Å, c = 32.83 Å, Z = 3
Identification
Color	Yellow, burnt orange, brown, black
Twinning	On {0001}
Cleavage	Perfect on {0001}
Tenacity	Moderately flexible
Mohs scale hardness	2
Luster	Vitreous to dull
Streak	Very pale yellow to white
Diaphaneity	Transparent
Specific gravity	2.32
Optical properties	Uniaxial (−)
Refractive index	n = 1.546
Pleochroism	Distinct; O = yellow; E = very pale yellow
Ultraviolet fluorescence	Non-fluorescent

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.^[3] The formula was significantly revised in 1996, identifying sodium as a previously unknown constituent.

^ Nickel, Ernest H. "IMA/CNMNC List of Mineral Names" (PDF). Materials Data, Inc. Retrieved May 6, 2012.
^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
^ ^a ^b ^c ^d ^e ^f ^g ^h "Shigaite". Mindat. Retrieved April 20, 2012.
^ ^a ^b ^c ^d "Shigaite Mineral Data". Webmineral. Retrieved May 20, 2012.
^ ^a ^b ^c ^d ^e ^f ^g ^h "Shigaite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved April 20, 2012.

[CNMNC_list-1] Nickel, Ernest H. "IMA/CNMNC List of Mineral Names" (PDF). Materials Data, Inc. Retrieved May 6, 2012.

[2] Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.

[mindat-3] ^ ^a ^b ^c ^d ^e ^f ^g ^h "Shigaite". Mindat. Retrieved April 20, 2012.

[webmineral-4] "Shigaite Mineral Data". Webmineral. Retrieved May 20, 2012.

[handbook-5] ^ ^a ^b ^c ^d ^e ^f ^g ^h "Shigaite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved April 20, 2012.

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