Jennite
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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.[1] It typically occurs as vein and open space fillings as a late mineral phase.[2] 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.[1]
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.[3]
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.[4]
Jennite transforms to metajennite at Script error: No such module "convert". by losing four water molecules.[3]
Cement chemistry
Script error: No such module "Unsubst". 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:
- Other calcium aluminium silicate hydrate (C-A-S-H) minerals:
References
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- Bibliography
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Further reading
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