There are 2 basic types of natural fractures that need to be studied when characterising naturally fractured reservoirs - whether it be a geothermal or hydrocarbon reservoir. These are extension and shear fractures.
Pink (Devonian age) mudstones on the bank of the River Tay (Perthshire, UK) are intensively fractured - including joints and larger through going fractures Here we look at some of their characteristics including some splaying geometries.