Abstract: Rhodochrosite has been discovered as a minor component of two manganese deposits in Scotland. At Islay it occurs as coatings and veinlets on and within hollandite-pyrolusite-hematite-goethite mineralisation. Two foram microfossils were found within the carbonate which is considered to have formed from the interaction of organic-rich groundwater and seawater. The Dalroy rhodochrosite has the form of stromatactis-like cavity infill structures and veinlets in a mineralogically complex manganese-iron ore in which braunite, bustamite, manganoan ilmenite and pyrophanite have been identified. Intergrowths of rhodochrosite and native copper grains occur in a calcite matrix within the infill structures. These intergrowths are typically one micrometre across, but achieve diameters of up to 50 µm. The genesis of the Dalroy rhodochrosite is more problematical, although a hydrothermal source is most likely.