Jennite

{{Short description|Inosilicate alteration mineral in metamorphosed limestone and in skarn}} {{Infobox mineral | name = Jennite | category = Silicate mineral | boxwidth = | boxbgcolor = | image = Jennite_CSH_3D_Crystal_Structure_RasMol.gif | imagesize = 260px | caption = Crystal structure of jennite: elementary unit cell viewed in 3D | formula = Ca₉Si₆O₁₈(OH)₆·8H₂O | IMAsymbol = Jnn<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 = 1,063 g/mol | strunz = 9.DG.20 | system = Triclinic | class = Pinacoidal ({{overline|1}}) <br/><small>(same H-M symbol)</small> | symmetry = ''P''{{overline|1}} | unit cell = a = 10.56, b = 7.25 <br/>c = 10.81&nbsp;[Å]; α = 99.7° <br/>β = 97.67°, γ = 110.07°; Z&nbsp;=&nbsp;1 | color = White | habit = Blade shaped crystals, fibrous aggregates, platy – sheet forms | twinning = | cleavage = Distinct on [001] | fracture = | tenacity = | mohs = 3.5 | luster = Vitreous (glassy) | polish = | refractive = n_α = 1.548 – 1.552 n_β = 1.562 – 1.564 n_γ = 1.570 – 1.571 | opticalprop = Biaxial (−) | birefringence = δ = 0.022 | 2V = Measured: 74° | dispersion = | pleochroism = | fluorescence= Weak white | absorption = | streak = White | gravity = | density = 2.32–2.33 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = | references = <ref name=Webmin>[http://webmineral.com/data/Jennite.shtml Jennite on Webmineral]</ref><ref name=Mindat>[http://www.mindat.org/min-2087.html Jennite on Mindat]</ref><ref>[http://rruff.geo.arizona.edu/AMS/result.php?mineral=Jennite Jennite in the American Mineralogist Crystal Structure Database]</ref><ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/jennite.pdf Handbook of Mineralogy]</ref> }}

'''Jennite''' is a calcium silicate hydrate mineral of general chemical formula: Ca₉Si₆O₁₈(OH)₆·8H₂O.

Jennite occurs as an alteration mineral in metamorphosed limestone and skarn.<ref name=Mindat/> It typically occurs as vein and open space fillings as a late mineral phase.<ref name=HBM/> It also occurs in hydrated cement paste.

A first specimen of jennite found in 1966 at the Crestmore quarries (Crestmore, Riverside County, California, US) was analysed and identified as a new mineral by Carpenter in 1966 (Carpenter, 1966). They named it in honor of its discoverer: Clarence Marvin Jenni (1896–1973) director of the Geological Museum at the University of Missouri.<ref name=Mindat/>

In contrast to the first analysis made by Carpenter, jennite was found to not contain appreciable amount of sodium when the Crestmore specimen was reexamined.<ref name=Gard>{{Citation | last1 = Gard | first1 = J.A. | last2 = Taylor | first2 = H.F.W. | last3 = Cliff | first3 = G. | last4 = Lorimer | first4 = G.W. | year = 1977 | title = A reexamination of jennite | periodical = American Mineralogist | series = | volume = 62 | pages = 365–368 | url = http://www.minsocam.org/ammin/AM62/AM62_365.pdf | doi = | accessdate = 2009-02-04 }}</ref>

The structure of jennite is made of three distinct modules: ribbons of edge-sharing calcium octahedra, silicate chains of wollastonite-type running along the b axis, and additional calcium octahedra on inversion centers. The hydroxyl groups are bonded to three calcium cations while no SiOH groups are observed.<ref>{{Citation | last1 = Carpenter | first1 = A.B. | last2 = Chalmers | first2 = R.A. | last3 = Gard | first3 =J.A. | last4 = Speakman | first4 = K. | last5 = Taylor | first5 = H.F.W. | year = 1966 | title = Jennite, a new mineral | periodical = American Mineralogist | series = | volume = 51 | pages = 56–74 | url = http://www.minsocam.org/ammin/AM62/AM62_365.pdf | doi = | accessdate = 2009-02-04 }}</ref> Jennite transforms to metajennite at {{convert|70|–|90|C}} by losing four water molecules.<ref name=Gard/>

==Cement chemistry== {{unsourced|section|date=August 2018}} Jennite is often used in thermodynamical calculations to represent the pole of the less evolved calcium silicate hydrate (C-S-H). The value of its atomic Ca/Si or molecular CaO/SiO₂ (C/S) ratio is 1.50 (9/6), as directly calculated from its elementary composition formula. Tobermorite represents the more evolved pole with a C/S ratio of 0.83 (5/6).

==See also==

* Other calcium silicate hydrate (C-S-H) minerals: ** Afwillite ** Gyrolite ** Thaumasite ** Tobermorite * Other calcium aluminium silicate hydrate (C-A-S-H) minerals: ** Tacharanite ** Hydrogarnet ** Hydrogrossular ** Hydrotalcite ** Katoite

==References== {{Reflist}}

;Bibliography * {{Citation | last1 = Abdul-Jaber | first1 = Q.H. | last2 = Khoury | first2 = H. | year = 1998 | title = Unusual mineralisation in the Maqarin Area (North Jordan) and the occurrence of some rare minerals in the marbles and the weathered rocks | periodical = Neues Jahrb. Geol. Paläontol. Abh. | volume = 208 | pages = 603–629 | url = | doi = }}

* {{Citation | last1 = Bonaccorsi | first1 = E. | last2 = Merlino | first2 = S. | last3 = Taylor | first3 = H.F.W. | year = 2004 | title = The crystal structure of jennite, Ca₉Si₆O₁₈(OH)₆&nbsp;·&nbsp;8&nbsp;H₂O, Locality: Fuka, Japan | periodical = Cement and Concrete Research | volume = 34 | pages = 1481–1488 | url = http://rruff.geo.arizona.edu/AMS/result.php?mineral=Jennite | doi = 10.1016/j.cemconres.2003.12.033 | accessdate = 2009-02-04 | issue = 9 | url-access = subscription }}

==Further reading== * {{Citation | last = Chen | first = Jeffrey J. |author2=Jeffrey J. Thomas |author3=Hal F.W. Taylor |author4=Hamlin M. Jennings | year = 2004 | title = Solubility and structure of calcium silicate hydrate | journal = Cement and Concrete Research | volume = 34 | issue = 9 | pages = 1499–1519 | doi = 10.1016/j.cemconres.2004.04.034 | issn = 0008-8846 | citeseerx = 10.1.1.568.4216 }} * {{Citation | last = Eakle | first = Arthur S. | year = 1927 | title = Famous mineral localities: Crestmore, Riverside County, California | journal = American Mineralogist | volume = 12 | pages = 319–321 | url = http://www.minsocam.org/MSA/collectors_corner/arc/crestmoreca1.htm | accessdate = 2009-11-01 }} * {{Citation | last = Naomichi | first = Hara | year = 2000 | title = Formation of jennite and tobermorite from amorphous silica | journal = J. Soc. Inorg. Mater. Japan | volume = 7 | issue = 285 | pages = 133–142 | issn = 1345-3769 | url = http://sciencelinks.jp/j-east/article/200011/000020001100A0298196.php | accessdate = 2009-02-04 | archive-date = 2012-02-17 | archive-url = https://web.archive.org/web/20120217004545/http://sciencelinks.jp/j-east/article/200011/000020001100A0298196.php | url-status = dead }} * {{Citation | last = Merlino | first = S. |author2=Bonaccorsi E. |author3=Armbruster T. | title = The real structure of tobermorite 11A: normal and anomalous forms, OD character and polytypic modifications (Note: MDO2 – synchrotron radiation source. Locality: Bascenov, Urals, Russia) | journal = European Journal of Mineralogy | volume = 13 | issue = 3 | year = 2001 | pages = 577–590 | url = http://rruff.geo.arizona.edu/AMS/minerals/Tobermorite | doi=10.1127/0935-1221/2001/0013-0577 | bibcode=2001EJMin..13..577M| url-access = subscription }} {{commonscat|Jennite}}

Category:Calcium compounds Category:Calcium minerals Category:Cement Category:Crestmore Heights, California Category:Geology of Riverside County, California Category:Octahydrate minerals Category:Inosilicates Category:Minerals in space group 2 Category:Triclinic minerals