Tobermorite

Tobermorite
Crystalline mass of tobermorite
General
CategorySilicate mineral,
Calcium silicate hydrate
FormulaCa5Si6O16(OH)2·4H2O, or;
Ca5Si6(O,OH)18·5H2O
IMA symbolTbm
Strunz classification9.DG.10
Crystal systemOrthorhombic
Crystal classDisphenoidal (222)
H-M symbol: (2 2 2)
Space groupC2221 (no. 20)
Unit cella = 11.17 Å, b = 7.38 Å
c = 22.94 Å; β = 90°; Z = 4
Identification
Formula mass702.36 g/mol
ColorPale pinkish white, white, brown
Crystal habitAs minute laths; fibrous bundles, rosettes or sheaves, radiating or plumose, fine granular, massive.
Cleavage{001} Perfect, {100} Imperfect
Mohs scale hardness2.5
LusterVitreous, silky in fibrous aggregates
StreakWhite
DiaphaneityTranslucent to translucent
Specific gravity2.423 – 2.458
Optical propertiesBiaxial (+)
Refractive indexnα = 1.570 nβ = 1.571 nγ = 1.575
Birefringenceδ = 0.005
Ultraviolet fluorescenceFluorescent, Short UV:weak white to yellow, Long UV:weak white to yellow
References

Tobermorite is a calcium silicate hydrate mineral with chemical formula: Ca5Si6O16(OH)2·4H2O or Ca5Si6(O,OH)18·5H2O.

Two structural varieties are distinguished: tobermorite-11 Å and tobermorite-14 Å. Tobermorite occurs in hydrated cement paste and can be found in nature as an alteration mineral in metamorphosed limestone and in skarn. It has been reported to occur in the Maqarin Area of north Jordan and in the Crestmore Quarry near Crestmore Heights, Riverside County, California.

Tobermorite was first described in 1880 for an occurrence in Scotland, on the Isle of Mull, around the locality of Tobermory.

Use in Roman concrete

Aluminum-substituted tobermorite is understood to be a key ingredient responsible for the longevity of ancient undersea Roman concrete. The volcanic ash that Romans used for construction of sea walls contained phillipsite, and an interaction with sea water caused the crystalline structures in the concrete to expand and strengthen, making that material substantially more durable than modern concrete when exposed to sea water.

Crystal structure of tobermorite: elementary unit cell.

Cement chemistry

Tobermorite is often used in thermodynamical calculations to represent the pole of the most evolved calcium silicate hydrate (C-S-H). According to its chemical formula, its atomic Ca/Si or molar CaO/SiO2 (C/S) ratio is 5/6 (0.83). Jennite represents the less evolved pole with a C/S ratio of 1.50 (9/6).

See also

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ↑ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Tobermorite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 27 July 2022.
  3. 1 2 "Mineralogy Database". mindat.org. Retrieved 27 July 2022.
  4. ↑ Barthelmy, David (2014). "Lavendulan Mineral Data". Webmineral.com. Retrieved 27 July 2022.
  5. ↑ Scottish physician and amateur mineralogist Matthew Forster Heddle (1828–1897) first described tobermorite in: Heddle (1880). "Preliminary notice of substances which may prove to be new minerals. Part second". Mineralogical Magazine and Journal of the Mineralogical Society. 4: 117–123. doi:10.1180/minmag.1880.004.18.04. See pp. 119–121.
  6. ↑ Ancient Romans made world’s ‘most durable’ concrete. We might use it to stop rising seas, Washington Post, Ben Guarino, July 4, 2017. Retrieved July 5, 2017.
  7. ↑ Ancient lessons: Roman concrete durable, green, Jim Destefani, ed., Ceramic Tech Today, The American Ceramic Society, June 7, 2013
  8. ↑ Jackson, Marie D.; Mulcahy, Sean R.; Chen, Heng; Li, Yao; Li, Qinfei; Cappelletti, Piergiulio; Wenk, Hans-Rudolf (2017). "Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete". American Mineralogist. 102 (7): 1435–1450. Bibcode:2017AmMin.102.1435J. doi:10.2138/am-2017-5993CCBY. ISSN 0003-004X.

Further reading