{{Short description|Zeolite mineral}} {{Infobox mineral | name = Gonnardite | category = Tectosilicate minerals | group = Zeolite group, natrolite subgroup | image = gonnardite.jpg | imagesize = 260px | caption = Gonnardite from the Bundoora Quarry, Victoria, Australia. Specimen size 4.9 cm | formula = (Na,Ca)<sub>2</sub>(Si,Al)<sub>5</sub>O<sub>10</sub>·3H<sub>2</sub>O | IMAsymbol = Gon<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 = 9.GA.05 (10 ed) <br /><small>8/J.21-40 (8 ed)</small> | dana = 77.1.5.7 | system = Tetragonal | class = Scalenohedral ({{overline|4}}2m) <br />H-M symbol: ({{overline|4}} 2m) | symmetry = ''I''{{overline|4}}2d | unit cell = a = 13.38 <br />c = 6.66&nbsp;[Å]; Z&nbsp;=&nbsp;2 | color = Colorless, white, yellow or pink to salmon orange | habit = Radiating fibrous; massive | twinning = | cleavage = | fracture = | tenacity = | mohs = 4 to 5 | luster = Vitreous to silky or dull | refractive = n<sub>α</sub> = 1.514, n<sub>β</sub> = 1.515, n<sub>γ</sub> = 1.520 | opticalprop = Biaxial (+) | 2V = Measured, 52° | birefringence = δ = 0.006 | pleochroism = | streak = White | gravity = 2.21 to 2.36 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Translucent | other = | references = <ref name=Mindat>{{Cite web|url=http://www.mindat.org/min-1724.html|title = Gonnardite}}</ref><ref name=Webmin>{{Cite web|url=http://www.webmineral.com/data/Gonnardite.shtml|title = Gonnardite Mineral Data}}</ref><ref name=HOM>{{cite web |last1=Anthony |first1=John W. |last2=Bideaux |first2=Richard A. |last3=Bladh |first3=Kenneth W. |last4=Nichols |first4=Monte C. |title=Gonnardite |url=http://www.handbookofmineralogy.org/pdfs/gonnardite.pdf |website=Handbook of Mineralogy |publisher=Mineral Data Publishing |access-date=13 March 2022 |date=2005}}</ref><ref name=Dana>Gaines et al (1997) Dana's New Mineralogy, Wiley</ref> }}

'''Gonnardite''' is a comparatively rare, fibrous zeolite, natrolite subgroup. Older papers claim that a complete solid solution exists between tetranatrolite and gonnardite, but tetranatrolite was discredited as a separate species in 1999.<ref name=AM84>American Mineralogist (1999) 84: 1445–1450</ref> A series, based on the disorder of the silicon-aluminum in the framework, appears to exist between Na-rich gonnardite and natrolite, Na<sub>2</sub>(Si<sub>3</sub>Al<sub>2</sub>)O<sub>10</sub>·2H<sub>2</sub>O.<ref name=ZOW>Tschernich, Zeolites of the World (1992) Geoscience Press, pages 215 to 225</ref>

Gonnardite was named in 1896 after Ferdinand Pierre Joseph Gonnard<ref name=GON>{{Cite web |url=http://www.minrec.org/labels.asp?colid=1316 |title=Archived copy |access-date=2010-03-30 |archive-date=2014-07-29 |archive-url=https://web.archive.org/web/20140729151344/http://www.minrec.org/labels.asp?colid=1316 |url-status=dead }}</ref> (1833–1923), who was Professor of Mining Engineering at the University of Lyon, France.

==Crystallography== Orthorhombic-bipyramidal class 2/m 2/m 2/m and tetragonal-scalenoidal class {{Overline|4}}2m (orthorhombic with a very close to b, or tetragonal with a equal to b). <br />Unit Cell Parameters: a = b = 13.21&nbsp;Å, c = 6.622&nbsp;Å, Z = 2<ref name=Webmin/><ref name=HOM/><ref name=MM62>Mineralogical Magazine (1998) 62: 548</ref><br />Space Group: I{{Overline|4}}2d

==Crystal habit== Crystals are prismatic, bounded by {110} and {111} as well as {100} and {001},<ref name=ZOW/> and gonnardite also occurs as radial hemispheres. Commonly found as zoned prisms or aggregates with thomsonite, natrolite and paranatrolite.<ref name=ZOW/>

==Structure== Gonnardite is a tectosilicate belonging to the natrolite group. The natrolite minerals are composed of chains of AlO<sub>4</sub> and SiO<sub>4</sub> tetrahedra that link to form frameworks. As with all zeolites, there are channels within the framework, and for the natrolite minerals the channels are occupied by polyhedra containing sodium, calcium or barium, together with oxygen and water.<ref name=AM77>American Mineralogist (1972) 77:685</ref> Gonnardite has the same framework structure as natrolite, but a disordered Si, Al distribution on the tetrahedral sites.<ref name=MM62/> Some of the water sites in the disordered natrolite structure of gonnardite are empty.<ref name=ZOW/>

==Environment== Gonnardite has been found in silica-poor volcanics and pegmatites. It occurs with thomsonite and natrolite in vesicles in the volcanic rock of The Nut, near Stanley, Tasmania, Australia, intergrown with natrolite at Don Hill, Tasmania and in drill holes with chabazite and calcite near Guildford, Tasmania.<ref name=AJM>Australian Journal of Mineralogy (2004) 10-2: 59–72</ref> It is also found in nepheline-syenite in the Grenville Geological Province, which is part of the Canadian Shield.<ref name=MinRec>The Mineralogical Record 37-4: 285</ref> The type locality (the place where the mineral was first described) is La Chaux de Bergonne, Gignat, Saint-Germain-Lembron, Puy-de-Dôme, Auvergne, France, and type material from this locality is held at the Natural History Museum, London, England, registration number BM.1930,166.

==References==

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Category:Natrolite subgroup Category:Tetragonal minerals Category:Minerals in space group 122