A talc or talc-like unit forms part of the structure of mica, illite and hydro-mica, vermiculite, montmorillonite and chlorite as well as tale and pyrophyllite. Transitions should be possible between these structures by chemical and/or thermal methods. Many such transitions have been observed in nature but comparatively few successful transitions have been carried out in the laboratory.

One aspect that has recently been under investigation at Leeds University Physics Department is the transition chlorite→mica. Treatment of a penninite by various acid media either with or without heat treatment failed to remove the brucite layer from the chlorite without also attacking the talc layers. No mica or talc-type of mineral was observed as an intermediate product, and a decrease of only 0.4 kX occurred in the spacing of the layers during acid attack.