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.
Mudstones can be extensively fractured - this blog looks at some characteristics of fractures inlcuding connected networks and plumose structures in the Cromlix Mudstone, near Stanley, Perthshire, UK.
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.