A Ni-Co-As ore sample from Cobalt City, Ontario, Canada, was examined with scanning electron microscopy and energy dispersive X-ray analysis. In addition to cobaltian pararammelsbergite with variable cobalt content, for which Cobalt City is the type locality, and erythrite, one new mineral was observed for this locality. Well-formed crystals of arsenolite, As(2)O(3), were found embedded in what appears to be fibrous spherocobaltite, CoCO(3). Additional information was obtained by Raman microscopy, confirming the identification of the arsenolite. Both are considered to be secondary minerals formed by exposure to air resulting in oxidation and the formation of secondary carbonates.