Early diagenetic concretions, that have grown in the last 130 years are common at Penpol in the Gannel Estuary. They are mineralogically complex, being dominated by calcite-siderite-Fe monosulphide cements. Commonly, they are nucleated around discarded metal artefacts. in one of the concretions, diageneticsimonkolleite (Zn(5)(OH)(8)Cl(2).H(2)O) has been identified along with zincite and an unnamed Zn phased this is the first record of simonkolleite in the UK. The diagenetic simonkolleite probably formed as a result of the corrosion of a Zn plate artefact within the estuary, either from shipping or possibly mine waste slag.