FINGERPRINTING TALC, TALC ORE AND TALC PRODUCTS BY COMPOSITION AND MINERAL ASSEMBLAGE

Talc has historically and is currently used in a wide variety of commercial products, and there is ongoing litigation with purported asbestos content of these products. Our goal in this project is to develop methods to be able to determine the source of a talc product either in raw form or when removed from a human lung. The scope of this project is to determine the provenance of talc products by identifying compositional fingerprints. Some of the samples are ore with known origins, serving as a control. Other samples are milled products with known locations and some are commercial products, of which the provenance is unknown.

Talc is mined from numerous locations in the US and internationally. Despite having common uses, not all talc products share the same composition. Talc, when referred to as a product may be talc ore, which includes significant amounts of other minerals, or may be almost entirely talc. Much of this depends on the protolith; talc is formed from deposits of hydrothermally altered carbonates, or metamorphosed ultramafic rocks. The metamorphic grade will also control the formation of amphiboles. The remnant composition from the protolith may be useful in tracing the talc products back to the type of deposits where they were formed.

Commercial talc samples were analyzed with x-ray fluorescence spectrometry and powder x-ray diffraction in order to determine the bulk composition and mineral assemblages. The XRF results indicate that ultramafic-sourced talc products contain significantly more transition metals than those from carbonate deposits. The bulk composition of these products distinguishes carbonate-derived talc based on a higher loss on ignition, determined by mass compared to the ultramafic derived samples. Microprobe analysis with wavelength dispersive and energy dispersive spectroscopy capabilities was used to identify the composition of individual mineral grains in the samples. The results show small differences in the major element concentrations with the exception of iron. Mineral assemblages including chlorite and iron oxides are present in samples from an ultramafic derived deposit. Carbonate derived products contain magnesite, calcite, and dolomite.