Mineralogy and Genesis of the Vermiculite Deposits at Libby, Montana

The problem considered in this report is one of the mineralogy and mode of formation of the extremely pure, large bodies of vermiculite. Mineralogically the ultrabasic intrusive, with which the economic mineral is associated, presents an array of rather unusual minerals. The determination of these minerals, their associations, and the sequence of alteration that lead to the formation of the vermiculite bodies, constitutes the problem.