Bath stone is an Oolitic Limestone composed of grain like fragments of calcium carbonate which resemble a fish roe in appearance. During the Jurassic Period (195 to 135 million years ago) when the Bath area was covered by a shallow sea and the marine sediment was laid down, each little grain became coated with lime as it was rolled around the sea bed. When highly magnified, the grains or Ooliths often reveal small shell or rock fragments along with decayed skeletons of marine life!
Apart from its pleasant appearance, a major feature of the stone is that it is a freestone, that is one which can be sawn or 'squared up' in any direction. Its beauty, close proximity, and manageability has ensured its appeal as a building material, and is literally the basic building block of Bath's lasting appeal.