The thermal reactivity of the naturally occurring silicates jadeite, NaAl[Si2O6], and nephrite, a variety of actinolite, Ca2 (Mg,Fe)5[(OH,F)Si4O11]2, have been investigated by thermogravimetric and thermomechanical analysis as well as temperature-dependent X-ray diffraction
and analytical electron microscopy. TG shows that nephrite undergoes a weight loss at around 900°C. Mass spectrometry reveals
that this irreversible reaction corresponds to the evolution of H2O, and XRD shows that a phase related to diopside CaMg[Si2O6] is formed. Jadeite does not undergo and observable weight changes up to 1000°C. Thermomechanical analysis indicates a reversible
phase transition at about 950°C. Temperature-dependent X-ray diffraction shows that jadeite is again present on cooling (peak
temperature: 1000°C), but that this is accompared by an additional unidentified phase. The mechanism of this process is not
yet clear although it has been observed in several samples from different origins and with different metal impurities.