Jennite

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Jennite
Jennite CSH 3D Crystal Structure RasMol.gif
Crystal structure of jennite: elementary unit cell viewed in 3D
General
CategorySilicate mineral
Formula
(repeating unit)		Ca9Si6O18(OH)6·8H2O
Strunz classification9.DG.20
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Unit cella = 10.56, b = 7.25
c = 10.81 [Å]; α = 99.7°
β = 97.67°, γ = 110.07°; Z = 1
Identification
Formula mass1,063 g/mol
ColorWhite
Crystal habitBlade shaped crystals, fibrous aggregates, platy - sheet forms
CleavageDistinct on [001]
Mohs scale hardness3.5
LusterVitreous (glassy)
StreakWhite
DiaphaneityTransparent to translucent
Density2.32 – 2.33
Optical propertiesBiaxial (-)
Refractive indexnα = 1.548 - 1.552 nβ = 1.562 - 1.564 nγ = 1.570 - 1.571
Birefringenceδ = 0.022
2V angleMeasured: 74°
Ultraviolet fluorescenceWeak 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: (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 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[]

References[]

  1. ^ Jennite on Webmineral
  2. ^ a b c Jennite on Mindat
  3. ^ Jennite in the American Mineralogist Crystal Structure Database
  4. ^ a b 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., vol. 208, pp. 603–629
  • Carpenter, A.B.; Chalmers, R.A.; Gard, J.A.; Speakman, K.; Taylor, H.F.W. (1966), "Jennite, a new mineral" (PDF), American Mineralogist, vol. 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, vol. 62, pp. 365–368, retrieved 2009-02-04

Further reading[]

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