{{Short description|Zeolite mineral series}} {{Infobox mineral | name = Gmelinite | category = Tectosilicate minerals | group = Zeolite group | image = Gmelinite-Na-Chabazite-Ca-153544.jpg | imagesize = 260px | caption = | formula = {{chem2|Na4(Si8Al4)O24*11H2O}}<ref name = IMA>{{Cite web|url=http://rruff.info/ima|title=IMA Mineral List with Database of Mineral Properties}}</ref> | IMAsymbol = Gmelinite-Na: Gme-Na<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 = 2,000.77 g | strunz = 9.GD.05 (10 ed) <br/><small>8/J.26-50 (8 ed)</small> | dana = 77.1.2.6 | system = Hexagonal | class = Dihexagonal dipyramidal (6mmm) <br/>H-M symbol: (6/m 2/m 2/m) | symmetry = ''P''6<sub>3</sub>/mmc | unit cell = a = 13.78, c = 10.03&nbsp;[Å]; Z&nbsp;=&nbsp;4 | color = Colorless, white, yellow, orange, pale green, pink, red, brown and grey | habit = Hexagonal plates, or short prisms, showing hexagonal dipyramids, pyramids and basal pinacoid. {10{{overline|1}}0}, {10{{overline|1}}1} and {0001} dominant. May also be tabular or rhombohedral. Crystals are striated parallel to (0001) | twinning = Interpenetrant twins common<ref name = RCP>Roberts, Campbell and Rapp (1990) Encyclopedia of Minerals, 2nd edition </ref> on {10{{overline|1}}1}. The twins consist of four individuals, three are at 90° to the other and at 60° to each other<ref name = Dana/> | cleavage = Good on {10{{overline|1}}0} | fracture = Conchoidal | tenacity = Brittle | mohs = {{frac|4|1|2}} | luster = Dull to vitreous | refractive = n<sub>ω</sub> = 1.476 - 1.494, n<sub>ε</sub> = 1.474 - 1.480<ref name = RCP/> | opticalprop = Uniaxial (-) | birefringence = δ = 0.002 - 0.014 | pleochroism = | streak = White | gravity = 2.04 to 2.17 | density = | melt = | fusibility = | diagnostic = | solubility = Soluble in cold 10% HCl. | diaphaneity = Transparent, translucent or opaque | other = Piezoelectric. Barely detectable radioactivity. As with all zeolites, water is released on heating, and almost all has been expelled by 400&nbsp;°C. | references = <ref name=Webmin>{{Cite web|url=http://www.webmineral.com/data/Gmelinite-Na.shtml|title = Gmelinite-Na Mineral Data}}</ref><ref name=Mindat>http://www.mindat.org/min-6973.html Mindat.org</ref> }}

'''Gmelinite''' is a series of rare zeolite minerals. The most common member is gmelinite-Na; others are gmelinite-Ca and gmelinite-K. It is closely related to the very similar mineral chabazite. Gmelinite was named as a single species in 1825 after Christian Gottlob Gmelin (1792–1860) professor of chemistry and mineralogist from Tübingen, Germany, and in 1997 it was raised to the status of a series.<ref name = Deer>Deer, Howie and Zussman (2004) Rock-Forming Minerals Volume 4B:690-696</ref><br />Gmelinite-Na has been synthesised from Na-bearing aluminosilicate gels.<ref name = Deer/> The naturally occurring mineral forms striking crystals, shallow, six sided double pyramids, which can be colorless, white, pale yellow, greenish, orange, pink, and red. They have been compared to an angular flying saucer.

== Structure ==

The aluminosilicate framework is composed of tetrahedra linked to form parallel double six-membered rings stacked in two different positions (A and B) in the repeating arrangement AABBAABB. The framework has no Al-Si order.<ref name = Dana/> Within the structure there are cavities with a cross-section of up to 4&nbsp;Å, and also wide channels parallel to the c axis with a diameter of 6.4&nbsp;Å.<ref name = SS>Senderov and Shishakova (1967) Russian Chemical Bulletin 16-1:151</ref> Space group: P6<sub>3</sub>/mmc. Unit cell parameters:<ref name = RCP/> a=13.72&nbsp;Å, c=9.95&nbsp;Å, Z=4.

== Environment ==

Generally occurs in Si-poor volcanic rocks, marine basalts and breccias, associated with other sodium zeolites such as analcime, {{chem2|Na(Si2Al)O6*H2O}}, natrolite, {{chem2|Na2(Si3Al2)O10*2H2O}}, and chabazite-Na, {{chem2|Na2Ca(Si8Al4)O24*12H2O}}. It also occurs in Na-rich pegmatites in alkaline rocks, and as an alteration product in some nepheline syenite intrusions.<ref name = Deer/> No sedimentary gmelinite has been found.<ref name = Dana>Gaines et al (1997) Dana's New Mineralogy Eighth Edition</ref> It is generally assumed that it forms at low temperatures, less than 100&nbsp;°C.<ref name = Deer/> It is widespread as a hydrothermal alteration product of ussingite, {{chem2|Na2AlSi3O8(OH)}}, associated with gobbinsite, {{chem2|Na5(Si11Al5)O32*11H2O}}, gonnardite, {{chem2|(Na,Ca)2(Si,Al)5O10*3H2O}}, and chabazite-K.<ref name = Deer/>

== Notable localities == thumb|left|Gmelinite from Ireland Gmelinite-Na occurs extremely rarely at the Francon Quarry, Montreal, Canada, in sills of the igneous volcanic rock phonolite which are rich in dawsonite, {{chem2|NaAl(CO3)(OH)2}}.<ref name = MinRec37>Tarassoff, Peter, and Horvath, Lazlo and Elsa (2006) Mineralogical Record 37-1:35</ref> It occurs both as pure gmelinite-Na and interlayered with chabazite in water-quenched basalts in Western Tasmania.<ref name = AJM>Sutherland, F L and Bottrill, R S (2004) Zeolites of Western Tasmania, Australian Journal of Mineralogy 10-2: 59 - 72</ref>

Associated minerals include other zeolites, especially chabazite, quartz, aragonite and calcite.

== Distribution == Type Locality: Monte Nero, San Pietro, Montecchio Maggiore, Vicenza Province, Veneto, Italy. Also found in Australia, Canada, Czech Republic, Germany, Hungary, Japan, Russia, UK and US.<ref name = Mindat/>

== References == <!--- See Wikipedia:Footnotes on how to create references using <ref></ref> tags which will then appear here automatically --> {{Reflist}}

== External links == *[http://helios.princeton.edu/zeomics/cgi-bin/view_structure.pl?src=iza&id=GME Structure type GME]{{Dead link|date=December 2022 |bot=InternetArchiveBot |fix-attempted=yes }} *[https://web.archive.org/web/20050407022309/http://mineral.galleries.com/minerals/Silicate/gmelinit/gmelinit.htm Mineral galleries] *[http://www.mindat.org/min-1714.html Mindat]

{{Commons}}

Category:Sodium minerals Category:Calcium minerals Category:Aluminium minerals Category:Zeolite group Category:Hexagonal minerals Category:Minerals in space group 194 Category:Minerals described in 1825