Jennite

Jennite
Crystal structure of jennite: elementary unit cell viewed in 3D
General
Category Silicate mineral
Formula
(repeating unit)		 Ca9Si6O18(OH)6·8H2O
Strunz classification 9.DG.20
Crystal system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
Space group P1
Unit cell a = 10.56, b = 7.25
c = 10.81 [Å]; α = 99.7°
β = 97.67°, γ = 110.07°; Z = 1
Identification
Formula mass 1,063 g/mol
Color White
Crystal habit Blade shaped crystals, fibrous aggregates, platy - sheet forms
Cleavage Distinct on [001]
Mohs scale hardness 3.5
Luster Vitreous (glassy)
Streak White
Diaphaneity Transparent to translucent
Density 2.32 – 2.33
Optical properties Biaxial (-)
Refractive index nα = 1.548 - 1.552 nβ = 1.562 - 1.564 nγ = 1.570 - 1.571
Birefringence δ = 0.022
2V angle Measured: 74°
Ultraviolet fluorescence Weak white
References [1][2][3][4]

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.[2] It typically occurs as vein and open space fillings as a late mineral phase.[4] 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.[2]

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 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 (158–194 °F) by losing four water molecules (Gard, 1977).

Cement chemistry

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 Ca/Si or CaO/SiO2 (C/S) ratio is 1.5 (9/6). Tobermorite represents the more evolved pole with a C/S ratio of 0.83 (5/6).

See also

References

  1. ↑ Jennite on Webmineral
  2. 1 2 3 Jennite on Mindat
  3. ↑ Jennite in the American Mineralogist Crystal Structure Database
  4. 1 2 Handbook of Mineralogy
Bibliography
  • 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, pp. 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), pp. 1481–1488, doi:10.1016/j.cemconres.2003.12.033, retrieved 2009-02-04
  • Carpenter, A.B.; Chalmers, R.A.; Gard, J.A.; Speakman, K.; Taylor, H.F.W. (1966), "Jennite, a new mineral" (PDF), American Mineralogist, 51, pp. 56–74, retrieved 2009-02-04
  • Gard, J.A.; Taylor, H.F.W.; Cliff, G.; Lorimer, G.W. (1977), "A reexamination of jennite" (PDF), American Mineralogist, 62, pp. 365–368, 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, retrieved 2009-02-04
  • Eakle, Arthur S. (1927), "Famous mineral localities: Crestmore, Riverside County, California", American Mineralogist, 12: 319–321, 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, 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, Bibcode:2001EJMin..13..577M, doi:10.1127/0935-1221/2001/0013-0577
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