Brittle Structures Joints and Veins Examples of joints and veins. If you look at the photographs of rock outcrops, you’ll notice thin dark lines that cross the rock faces. These lines represent traces of natural cracks along which the rock broke and separated into two pieces during brittle deformation. Geologists refer to such natural cracks as joints (figure above a, b). Rock bodies do not slide past each other on joints. Since joints are roughly planar structures, we define their…
