The Stability of Tobermorite in the System CaO-SiO2-H2O at Elevated Temperatures and Pressures

K. Speakman
Building Research Station, Garston, Watford, Herts.

Summary: Hydrothermal studies in the silica-rich region of the CaO-SiO2-H2O system have given information on the stability field of tobermorite. At saturated steam pressures tobermorite is unstable relative to xonotlite (C6S6H) above 140 °C but between 10 000 and 40 000 lb/in.2 (69 and 276 N/mm2), the decomposition temperature is raised to 285±5 °C. Tobermorite is stable at all compositions between C/S = 0·67 and 1·0 up to this temperature and has a formula close to C5S6H5. Variable compositions reported earlier are thought to be mixtures rather than lime-rich or silica-rich tobermorites.

Data have also been collected on the equilibrium assemblages below C/S = 0·67 and between C/S = 1·0 and 1·5 involving truscottite, gyrolite, xonotlite, foshagite, and hillebrandite.

Mineralogical Magazine; December 1968 v. 36; no. 284; p. 1090-1103; DOI: 10.1180/minmag.1968.036.284.06
© 1968, The Mineralogical Society
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