Bluestone finishes are a choice you can make when buying bluestone. There are two basic surface finishes. Natural Cleft is slightly rough, Sawn Thermal is smooth but not slippery. Natural Cleft is split along natural fault lines and the result is a slightly rough texture with distinct raised and sunken areas. Sawn thermal is sawn and then heat treated for a smooth finish with no raised or sunken areas. Because sawn thermal is sawn and then heat treated it is typically more expensive than natural cleft.