Chemistry: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 |
| |re|er}} | 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 was found to not contain appreciable amount of sodium when the Crestmore specimen was reexamined.[6]
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.[7]
Jennite transforms to metajennite at 70–90 °C (158–194 °F) by losing four water molecules.[6]
Cement chemistry
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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:
- Tacharanite
- Hydrogarnet
- Hydrogrossular
- Hydrotalcite
- Katoite
References
- ↑ Jennite on Webmineral
- ↑ 2.0 2.1 2.2 Jennite on Mindat
- ↑ Jennite in the American Mineralogist Crystal Structure Database
- ↑ 4.0 4.1 Handbook of Mineralogy
- ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
- ↑ 6.0 6.1 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
- ↑ 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
- 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
- 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
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
- 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 (3): 577–590, doi:10.1127/0935-1221/2001/0013-0577, Bibcode: 2001EJMin..13..577M, http://rruff.geo.arizona.edu/AMS/minerals/Tobermorite
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