Eight scapolite samples from different geologie settings were selected so as to fully represent the marialite–meionite series.

Thermal analyses (TG and DTA), as well as mass spectrometer analysis with a heating device, were used to define the release of the volatile components during heating. In the temperature range up to 800° C, the emission of H2O, SO2, CO2, NaCl, and KCl was observed to occur continuously, but with five evident steps. The presence of SO2 in the gaseous phase may be due to decomposition reactions.

X-ray powder diffractograms recorded every 100° C during heating up to 800° C indicated an increase in a and V, which occurred linearly in the whole marialite–meionite series, with a trend inversely proportional to the percentage of meionite present in each sample.

The relationships between increases in lattice parameters, with rising temperature, and percentage of meionite may be expressed by the equations:

The trends in a and V are reversible since samples treated to 800° C revert to initial cell parameters upon cooling. Temperature increases did not clearly affect the value of c, which remained constant. Beyond 800° C the unit cell parameter a increased anomalously, in an irreversible way, while the breakdown of the mineral started producing various compounds: plagioclase, which invariably has a lower calcium content than the scapolite from which it derives, halite and calcium aluminum silicates.

Refractive index measurements carried out during heating and on the cooled sample, confirmed such behavior, at least to a first approximation, showing for both and ω a linear increase during heating and a reversal of this trend to the initial values upon cooling.

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