The thermal changes occurring in zeolites of the natrolite group have been investigated by DTA, TGA, and continuous-heating X-ray photography. This combination of techniques facilitated a better description of the dehydration phenomena. Several as yet unknown metaphases have been recorded, and stability ranges have been reassessed. Structurally, upon heating natrolite behaves entirely differently from its isotypes mesolite and scolecite which are mutually similar in behavior. Thomsonite and gonnardite also show similar X-ray diffraction powder patterns, with aspects of both natrolite and mesolite/scolecite. Edingtonite shows an individual pattern and is the only member of the group where heating does not result in a phase amorphous to X-rays (X-amorphous).
The only feature common to all members of the group is that the room temperature phase reacts upon heating by a considerable contraction along the a and b axes and a slight expansion along the c axis, in accordance with the general structure of the group.