Jennite

Jennite
Crystal structure of jennite: elementary unit cell viewed in 3D
General
Category	Silicate mineral, Calcium silicate hydrate (CSH)
Chemical formula	Ca9Si6O18(OH)6·8H2O
Identification
Molar mass	1062
Color	White
Crystal habit	Blade shaped crystals, fibrous aggregates, platy - sheet forms
Crystal system	Triclinic, Space Group: P1
Cleavage	[001] Distinct
Mohs scale hardness	3.5
Luster	Vitreous (glassy)
Streak	White
Density	2.32 – 2.33
Ultraviolet fluorescence	Weak white
Other characteristics	Late stage mineral in metamorphosed limestone
References	[1][2][3]

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

Jennite occurs in hydrated cement paste and can be found in nature in particular conditions, e.g., as alteration mineral in metamorphosed limestone and skarn.

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

In contrast to the first analysis made by Carpenter, jennite does not contain appreciable amount of sodium when the Crestmore specimen was reexamined (Gard, 1977).

The structure of jennite determined by 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 (Bonaccorsi 2004).

Jennite transforms to metajennite at 70 – 90 °C by losing four water molecules.

See also

• Other Calcium silicate hydrate (CSH) minerals:
  • Afwillite
  • Thaumasite
  • Tobermorite
• Other Calcium aluminium silicate hydrate, (CASH) minerals:
  • Hydrogarnet
  • Hydrotalcite

References

• Abdul-Jaber, Q.H.; Khoury, H. (1998), "Unusual mineralisation in the Maqarin Area (North Jordan) and the occurrence of some rare minerals in the marbles and the weathered rocks", Neues Jahrb. Geol. Paläontol. Abh. 208: 603–629 

• Bonaccorsi, E.; Merlino, S.; Taylor, H.F.W. (2004), "The crystal structure of jennite, Ca₉Si₆O₁₈(OH)₆ · 8 H₂O, Locality: Fuka, Japan", Cement and Concrete Research 34 (9): 1481–1488, doi:10.1016/j.cemconres.2003.12.033, http://rruff.geo.arizona.edu/AMS/result.php?mineral=Jennite, retrieved 2009-02-04 

• Carpenter, A.B.; Chalmers, R.A.; Gard, J.A.; Speakman, K.; Taylor, H.F.W. (1966), "Jennite, a new mineral", American Mineralogist 51: 56–74, http://www.minsocam.org/ammin/AM62/AM62_365.pdf, retrieved 2009-02-04 

• Gard, J.A.; Taylor, H.F.W.; Cliff, G.; Lorimer, G.W. (1977), "A reexamination of jennite", American Mineralogist 62: 365–368, http://www.minsocam.org/ammin/AM62/AM62_365.pdf, retrieved 2009-02-04 

Further reading

• Chen, Jeffrey J.; Jeffrey J. Thomas, Hal F.W. Taylor, Hamlin M. Jennings (2004), "Solubility and structure of calcium silicate hydrate", Cement and Concrete Research 34 (9): 1499–1519, doi:10.1016/j.cemconres.2004.04.034, ISSN 0008-8846, http://www.sciencedirect.com/science/article/B6TWG-4CNH51T-1/2/7466036d6266db6640c8bcbcbee3bc9f, retrieved 2009-02-04 

• Eakle, Arthur S. (1927), "Famous mineral localities: Crestmore, Riverside County, California", American Mineralogist 12: 319–321, http://www.minsocam.org/MSA/collectors_corner/arc/crestmoreca1.htm, retrieved 2009-11-01 

• Naomichi, Hara (2000), "Formation of jennite and tobermorite from amorphous silica", J. Soc. Inorg. Mater. Japan 7 (285): 133–142, ISSN 1345-3769, http://sciencelinks.jp/j-east/article/200011/000020001100A0298196.php, retrieved 2009-02-04 

• Merlino, S.; Bonaccorsi E., Armbruster T. (2001), "The real structure of tobermorite 11A: normal and anomalous forms, OD character and polytypic modifications (Note: MDO2 - synchrotron radiation source. Locality: Bascenov, Urals, Russia)", European Journal of Mineralogy 13: 577–590, http://rruff.geo.arizona.edu/AMS/minerals/Tobermorite