Abstract
Naturally occurring opals from three different regions in Australia were studied for their thermal characteristics. All the opals showed initial expansion followed by contraction in thermomechanical analysis (TMA) although the temperature at which the change from expansion to contraction occurred depended on their provenance. Thermogravimetric analysis (TG) revealed different rates and temperatures of dehydration for these opals. A general correlation between the temperature at which there was a zero thermal expansion and that of the maximum rate of dehydration was observed. A dehydration–sintering mechanism is proposed with the effect of sintering being more pronounced following total dehydration.
Similar content being viewed by others
References
R. Webster, Gems, Their Sources Descriptions and Identification, Butterworths, 3rd ed., London 2000.
J. B. Jones and E. R. Segnit, J. Geol. Soc. Aust., 18 (1971) 57.
A. G. Smallwood, Chemical and Physical Evaluation of Australian Precious Opal, M.Sc, UTS, 1999, p. 43.
J. B. Jones and E. R. Segnit, Min. Mag., 37 (1969) 357.
D. M. McPherson and L. D. Pye, Glastech. Ber., 62 (1989) 208.
G. H. Frischat and R. Schwander, Geochim. Cosmochim., 53 (1989) 2731.
J. B. Jones and E. R. Segnit, Nature, 4886 (1963) 1191.
E. R. Segnit and T. J Stevens, J. Geol. Soc. Aust., 12 (1965) 211.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Brown, L.D., Ray, A.S., Thomas, P.S. et al. Thermal Characteristics of Australian Sedimentary Opals. Journal of Thermal Analysis and Calorimetry 68, 31–36 (2002). https://doi.org/10.1023/A:1014912331807
Issue Date:
DOI: https://doi.org/10.1023/A:1014912331807