Motukoreaite

{{Short description|Mineral}} {{Infobox mineral | name = Motukoreaite | category = Sulfate and Carbonate mineral | boxwidth = | boxbgcolor = | image = Motukoreaite-Phillipsite-91264.jpg | imagesize = 260px | caption = Yellow-white balls of motukoreaite held together by phillipsite | formula = Mg6Al3(OH)18[Na(H2O)6](SO4)2·6H2O (possibly more than one species) | IMAsymbol = Mtu<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = | strunz = 7.DD.35 | dana = 17.1.7.1 | system = Trigonal | class = Hexagonal scalenohedral ({{overline|3}}m) H-M symbol: ({{overline|3}} 2/m) | symmetry = ''R''{{overline|3}}m | unit cell = a = 9.172(2) Å, c = 33.51(1) Å, Z = 3 | color = Colorless, white, pale yellow, pale yellow-green | habit = | twinning = | cleavage = Good on {0001}, perhaps a parting | fracture = | tenacity = Sectile, flexible | mohs = 1–1.5 | luster = Dull | polish = | refractive = nα = 1.510, nβ = 1.510 | opticalprop = Uniaxial (+) | birefringence = δ = 0.012 | 2V = | dispersion = | pleochroism = | fluorescence= | absorption = | streak = White | gravity = 1.43–1.53 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Semitransparent | other = | references = <ref name=handbook>{{cite web|title=Motukoreaite|url=http://www.handbookofmineralogy.com/pdfs/motukoreaite.pdf|work=Handbook of Mineralogy|publisher=Mineral Data Publishing|accessdate=May 27, 2012}}</ref><ref name=mindat>{{cite web|title=Motukoreaite|url=http://www.mindat.org/min-2793.html|publisher=Mindat|accessdate=May 27, 2012}}</ref><ref name=Webmin>{{cite web|title=Motukoreaite|url=http://webmineral.com/data/Motukoreaite.shtml|publisher=Webmineral|accessdate=June 6, 2012}}</ref> }}

'''Motukoreaite''' is a mineral with formula Mg6Al3(OH)18[Na(H2O)6](SO4)2·6H2O (possibly more than one species).<ref>{{Cite book |first1=Malcolm E. |last1=Back |title=Fleischer's Glossary of Mineral Species |year=2014 |edition=11 |publisher=Mineralogical Record Inc. |pages=434 |location=Tucson AZ}}</ref> The mineral is named for Motukorea, the island in New Zealand where it was discovered. Motukoreaite was first noted in 1941 and officially described in 1977.

==Description== Motukoreaite occurs as claylike cement or hexagonal tabular crystals up to {{convert|0.2|mm|in|abbr=on}} in size that form rosettes, boxworks, and subparallel aggregates. The crystals are semitransparent and are white, pale yellow, pale yellow-green, or colorless. The mineral readily dehydrates partially.<ref name=handbook/>

Motukoreaite has been found in association with apatite, barite, calcite, chabazite, calcic plagioclase, gismondine, gypsum, hisingerite, hydrotalcite, limonite, magnetite, montmorillonite, nordstrandite, olivine, phillipsite, pyroxene, quartz, and zeolites.<ref name=handbook/>

==Formation== Motukoreaite forms from the alteration of submarine basaltic glass at temperatures below {{convert|150|C|F}}.<ref name=Z1058>Zamarreño, p. 1058.</ref> The alteration occurs in the sequence motukoreaite, phillipsite, calcite. A study in 1989 suggested that motukoreaite is a common, widely occurring mineral.<ref name=Z1054>Zamarreño, p. 1054.</ref>

==History== Motukoreaite was first identified as "beach limestone" by J. A. Bartrum in 1941 at two locations along the shore of Motukorea where it occurs as a coating or alteration of basaltic sand and basaltic tuff related to a small Pleistocene volcanic cone.<ref name=R389>Rodgers, p. 389.</ref> In 1977, the new mineral was officially described from the island and the name ''motukoreaite'' was approved by the Commission on New Minerals and Mineral Names in honor of the island. The mineral's small crystal size made determination of its optical properties difficult.<ref name=R390>Rodgers, p. 390.</ref>

==Distribution== Motukoreaite is known from Motukorea, New Zealand, La Piatta quarry in Italy, Stradner Kogel in Austria,<ref name=mindat/> and the western Mediterranean Sea near Spain.<ref name=Z1054/> It has been reported from the Surtsey Island and other locations on the mid-Atlantic Ridge. It also occurs along the axial rift of the Red Sea.<ref name=handbook/>

The type material is held at the University of Auckland in Auckland, New Zealand, the Natural History Museum, London, and the National Museum of Natural History in Washington, D.C.<ref name=handbook/>

==References== {{Reflist}}

===Bibliography=== *{{cite journal|last1=Rodgers|first1=K. A.|last2=Chisholm|first2=J. E.|last3=Davis|first3=R. J.|last4=Nelson|first4=C. S.|title=Motukoreaite, a new hydrated carbonate, sulphate, and hydroxide of Mg and Al from Auckland, New Zealand|journal=Mineralogical Magazine|date=September 1977|volume=41|issue=319|pages=389–390|url=http://www.minersoc.org/pages/Archive-MM/Volume_41/41-319-389.pdf|url-status=dead|publisher=The Mineralogical Society|doi=10.1180/S0026461X00038147|bibcode=1977MinM...41..389R|s2cid=251023642 |access-date=2012-06-03|archive-date=2016-05-27|archive-url=https://web.archive.org/web/20160527122003/http://www.minersoc.org/pages/Archive-MM/Volume_41/41-319-389.pdf}} *{{cite journal|last1=Zamarreño|first1=Isabel|last2=Plana|first2=Feliciano|last3=Vazquez|first3=Antonio|last4=Clague|first4=David A.|title=Motukoreaite: A common alteration product in submarine basalts|journal=American Mineralogist|date=October 1989|volume=74|issue=9–10|pages=1054–1058|url=http://www.minsocam.org/ammin/AM74/AM74_1054.pdf}}

==External links== {{Commonscat-inline|Motukoreaite}}

Category:Trigonal minerals Category:Minerals in space group 166 Category:Sodium minerals Category:Magnesium minerals Category:Aluminium minerals Category:Sulfate minerals Category:Carbonate minerals