Less well known, however, are the minerals that have been exposed in limestone quarries in west-central Illinois, including display-quality specimens of twinned calcite and the uncommon minerals violarite and polydymite.
Polydymite, a relatively rare mineral, has been confirmed in specimens from Hamilton by X-ray powder diffraction (White, 1970).
JOINT COMMITTEE ON POWDER DIFFRACTON STANDARDS (1974) Selected Powder Diffraction Data for Minerals: Millerite, polydymite and violarite.
Green gaspeite was tentatively identified by XRD as a constituent of a yellow-green secondary coating (mostly an unnamed Ni-Fe sulfate: see below) on pentlandite and polydymite.
Polydymite was identified by XRD as metallic gray material associated with pentlandite.
However, it may be polydymite; the composition needs checking.