FUNDAMENTAL STUDIES OF TALC. I. CONSTITUTION OF TALCS

The mineralogical constitution of as-mined talcs and the corresponding relationship to the chemical composition are reported. Results of a literature survey suggest the occurrence of solid solutions of molecules or groups of molecules. The solid solutions may be in the form of chlorite, serpentine, or SiO sub2 layers intermixed with the talc layers, andor double- chain or multichain molecules intermixed with the extended chain or larger structure of talc. Solid solutions of impurity ions for Mg and possibly for Si occur primarily in the admixed molecular groups. Both the molecular and ionic solid solutions can be responsible for the variations observed in as-mined talc. Chemical, x-ray diffraction, and differential thermal DTA analyses were made of talc samples obtained from the major US talc-producing areas. The DTA method appeared to be the most informative because of the sensitivity of the samples to thermal effects and the lack of complete dependence on structural regularity. The textural variations revealed by petrographic examinations may be related to structural modifications.