Is shale a hard rock or soft rock?
Shale is a fine-grained sedimentary rock whose original constituents were clay minerals or muds. It is characterized by thin laminae[1] breaking with an irregular curving fracture, often splintery and usually parallel to the often-indistinguishable bedding plane. This property is called fissility. Non-fissile rocks of similar composition but made of particles smaller than 1/16 mm are described as mudstones. Rocks with similar particle sizes but with less clay and therefore grittier are siltstones. Shale is the most common sedimentary rock.
