- Joints are produced by tensional forces. These forces may be a result of folding, cooling or unloading rocks.
- They give rocks a blocky appreance when they outcrop at the earths surface.
- Joints will only form in competent rocks, these are brittle and break when put under tension.
- Include: sandstone, limestone and grantie.
- Joints in sedimentary rocks are usually found perpendicular to the beds.
Joints formed by folding (Tectonic Joints)
- Produced by tension created in rocks when they are folded by earths movements.
- Compressive forces fold the rocks but cause some of the surrounding rocks to be put under tensional pressure.
- The rocks fracture because the outer surface of the bed is stretched more than the inner surface.
- The rock is conpetent so does not change thickness…