Joints, rock fissures which is a class of small faults, refers to both the rock to split and crack surface faults no relative displacement. Joints are a kind of fault structures widely developed in the upper rock of the Earth’s crust. According to their origins, they can be divided into two types,primary joints and secondary joints. Primary joints are formed during diagenetic processes.Secondary joints are formed after diagenesis of rock, including non-structural joints (weathered joints) and structural joints.

　　The joints which we can see in the granite body are structural joints and they are formed by crustal movement stress after the diagenesis of the granite body.

Do I make myself clear?

　　There are three sets of primary joints in granite: vertical joint, flat-lying joint and diagonal joint. The rock is cut by several sets of joints into some polyhedral fragments whose edges and corners are the first to be affected by temperature and water. As time goes by, with the corners gradually wearing away the rock becomes spherical or achieves spheroidicity.The phenomenon like this is called spheroidal weathering.