Chemistry: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[1] |
Strunz classification | 7.DD.35[2] |
Dana classification | 31.1.2.1[2] |
Crystal system | Trigonal |
Crystal class | Rhombohedral (3) H-M symbol: (3)[2] |
Space group | R3[3] |
Unit cell | a = 9.51 Å, c = 32.83 Å,[2] Z = 3[4] |
Identification | |
Color | Yellow, burnt orange, brown, black[4] |
Twinning | On {0001}[4] |
Cleavage | Perfect on {0001}[4] |
Tenacity | Moderately flexible[4] |
Mohs scale hardness | 2[4] |
|re|er}} | Vitreous to dull[2] |
Streak | Very pale yellow to white[4] |
Diaphaneity | Transparent[2] |
Specific gravity | 2.32[3] |
Optical properties | Uniaxial (−)[2] |
Refractive index | n = 1.546[3] |
Pleochroism | Distinct; O = yellow; E = very pale yellow[4] |
Ultraviolet fluorescence | Non-fluorescent[3] |
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.[2] The formula was significantly revised in 1996, identifying sodium as a previously unknown constituent.
Description
Shigaite occurs as hexagonal tabular crystals up to 2 cm (0.79 in) in size or as thin films and coatings. The mineral can be yellow, burnt orange, brown or black in color.[4] Shigaite occurs in metamorphosed deposits of manganese ore[4] and is the Mn2+ analogue of motukoreaite.[6]
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.[6]
History
Shigaite was discovered in 1985 in the Ioi Mine,[lower-alpha 1] Shiga Prefecture, Japan.[2] The original study, published in the journal Neues Jahrbuch für Mineralogie, Monatshefte,[1] identified the formula as Al4Mn7(SO4)2(OH)22·8H2O.[7] The formula was significantly revised in 1996 using a sample from the N'Chwaning Mine, South Africa.[6] 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.[8]
Distribution
(As of 2012), shigaite is known from the following sites:[2]
- 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.[4]
Association
Shigaite has been found associated with the following minerals:[4]
Ioi mine, Japan
|
Wessels Mine, South Africa
|
Iron Monarch, South Australia
|
Notes
References
- ↑ 1.0 1.1 Nickel, Ernest H.. "IMA/CNMNC List of Mineral Names". Materials Data, Inc.. http://pubsites.uws.edu.au/ima-cnmnc/IMA2009-01%20UPDATE%20160309.pdf.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 "Shigaite". Mindat. http://www.mindat.org/min-3638.html.
- ↑ 3.0 3.1 3.2 3.3 "Shigaite Mineral Data". Webmineral. http://webmineral.com/data/Shigaite.shtml.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 "Shigaite". Handbook of Mineralogy. Mineral Data Publishing. http://www.handbookofmineralogy.com/pdfs/shigaite.pdf.
- ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W. https://www.cambridge.org/core/journals/mineralogical-magazine/article/imacnmnc-approved-mineral-symbols/62311F45ED37831D78603C6E6B25EE0A.
- ↑ 6.0 6.1 6.2 Cooper, p. 91.
- ↑ 7.0 7.1 Hawthorne, Frank C. (November–December 1986). "New Mineral Names". American Mineralogist 71 (11 & 12): 1546. http://www.minsocam.org/ammin/AM71/AM71_1543.pdf. Retrieved May 17, 2012.
- ↑ Cooper, p. 96.
Bibliography
- Cooper, Mark A.; Hawthorne, Frank C. (February 1996). "The crystal structure of shigaite, (AlMn (super 2+)2 (OH)6)3 (SO4)2 Na(H2O)6 {H2O}6, hydrotalcite-group mineral". The Canadian Mineralogist 34 (1): 91–97. ISSN 0008-4476. http://rruff.geo.arizona.edu/doclib/cm/vol34/CM34_91.pdf. Retrieved May 23, 2012.
Further reading
- Pring, A.; Slade, P. G.; Birch, W. D. (September 1992). "Shigaite from Iron Monarch, South Australia". Mineralogical Magazine 56 (384): 417–419. doi:10.1180/minmag.1992.056.384.15. Bibcode: 1992MinM...56..417P. http://rruff.geo.arizona.edu/doclib/MinMag/Volume_56/56-384-417.pdf. Retrieved April 20, 2012.
Original source: https://en.wikipedia.org/wiki/Shigaite.
Read more |