Stone sculpture stone carving. Alabaster and softer kinds of serpentine, all about 3 on the Mohs scale, are more durable than soapstone. Alabaster, in particular, has long been cherished for its translucence. Limestone and sandstone, at about 4 on the Mohs scale, are the only sedimentary stones commonly carved. Limestone comes in a popular oolitic variety, about twice as hard as alabaster, that is excellent for carving. The harder serpentines can also reach 4 on the Mohs scale. Marble, travertine, and onyx are at about 6 on the Mohs scale. Marble has been the preferred stone for sculptors in the European tradition
Portland stone or "ooliths" (from the Greek for "egg-shaped" or "egg-stone"), became partially cemented together (or lithified) by more calcite, to form the oolitic limestone that is called Portland stone. The degree of cementation in Portland stone is such that the stone is sufficiently well cemented to allow it to resist weathering, but not so well cemented that it can't be readily worked (cut and carved) by masons. This is one of the reasons why Portland stone is so favoured as a monumental and architectural stone. Dr Geoff Townson conducted three years doctoral research on the Portlandian, being the first to describe