It may also form by hydrothermal alteration of rocks. It occurs with muscovite, chlorite, garnet, staurolite and kyanite. Its small grain size and superficial resemblance to chlorite makes it difficult to identify with certainty in the field, hence is frequently overlooked. Fe-rich chloritoid occurs in the argillites interbedded with the Waterloo quartzite exposed in the Waterloo area and adjacent Jefferson County. Olson also reports its prescence in quartzite to the south along the McCaslin Range.
Associated minerals are biotite, actinolite and stilpnomelane.