Jennite

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Jennite
Jennite CSH 3D Crystal Structure RasMol.gif
Crystal structure of jennite: elementary unit cell viewed in 3D
General
Category Silicate mineral
Formula
(repeating unit)
Ca9Si6O18(OH)6·8H2O
Strunz classification 09.DG.20
Crystal symmetry Triclinic, pinacoidal
H-M symbol: (1)
Space group: P1
Unit cell a = 10.56 Å, b = 7.25 Å, c = 10.81 Å; α = 99.7°, β = 97.67°, γ = 110.07°; Z=1
Identification
Formula mass 1063 g/mol
Color White
Crystal habit Blade shaped crystals, fibrous aggregates, platy - sheet forms
Crystal system Triclinic
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, 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.[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 by losing four water molecules (Gard, 1977).

See also[edit]

References[edit]

Notes
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: 603–629 
  • 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, 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, retrieved 2009-02-04 

Further reading[edit]