Abstract: Wollastonite is reported, for the first time in Iceland, in hydrothermally altered basaltic rocks in the Krafla high-temperature geothermal area, northern Iceland. Two possible modes of origin are suggested: (1) A contact metamorphic origin at the expense of hydrothermal quartz and calcite near the margins of dykes. (2) A hydrothermal origin at depths below 1000 m where fluid temperatures exceed 300 °C.