Only three types of joints are studied under classification of joints on basis of geometry; strike joints, dip joints and oblique joints. Hade joint is not a type of joint.

Tension joints are also produced in igneous rocks during ir cooling. Joints produced in many rocks during wearing of overlying strata and subsequent release of stresses by expansion are also thought to be due to tensile forces.

The polygonal cracks are thought to be directly related to tensile forces developed during cooling (accompanied by contraction) of hot molten material (lava).

Systematic joints show a distinct regularity in ir occurrence which can be measured and mapped easily.

Many landslides and slope failures are directly related to jointed nature of rocks. This is due to instability of rocks in hilly regions and jointed rocks get easily lubricated in presence of moisture and start sliding or falling from ir places.

We may find quite a large proportion of outcrop of any of se rocks practically free from joints at some places, but at or places same type of rock may be heavily jointed, showing cracks of greater variety. Hence it is not only genesis of rocks which responsible for se structures but also forces acting on m.

There may be or may not be an opening up of blocks perpendicular to joint planes. Hence joints may be of open or close nature.

The metamorphic rocks types are heavily jointed in many cases, joints being of irregular or non-systematic types. These joints are often result of local and regional stresses acting on rocks as a source of metamorphism.

Longitudinal or S joints, are joints traversing parallel to linear structure. In se rocks all joint systems traversing at any or angular inclination with linear structures are described as diagonal joints.

Non-systematic or irregular joints appear at random in rocks and may have incompletely defined surfaces. In many cases, se are related to systematic joints in that se occur between m.