Wollastonite and calcite. Lamellar (long, thin) crystals of Wollastonite (upper half) on calcite (lower half). Wollastonite is a white to greyish-white calcium-silicate mineral (CaSiO3). It forms by the conversion of limestone or dolomite under conditions of high pressure and temperature in the presence of silica bearing fluids. The lower half of the sample is calcite. Specimen found in Lappeenranta, Finland.