1. Joint may be defined as divisional planes or surfaces that divide rocks, and along which there has been no visible movement parallel to the plane or surface. They are fractures (fissures, partings, planes) where adjacent slabs and masses of bedrock join.
The term joint is said to have originated in the British coal fields because the miners thought the rocks were, joined along fractures, just as bricks are put together in a wall

4. DESCRIPTION:-
Joint occur at the outcrop scale in virtually all rocks and thus comprise the most abundant structural element in the earth’s crust. The length of the joints is measured in feet, tens of feet, or even hundreds of feet.
Joint show closely spaced as well as widely spaced and the distance between them is measured in inches or tens of feet. Although most joints are planes, some are curved surfaces. Most joints at least initially, are tight fractures. Slight movement at right angles to the joint or weathering may produce an open fissure also called gash fracture. Most joints are smooth, but some display plumose markings that are ridges and depressions a millimeter or so in height.
open fissure
plumose marks

5. Description
Wavy plumose structure on a joint in sandstone

6. Description
Attitude:-
Joints may have any attitude; some joints are vertical, others are horizontal, and many are inclined at various angles. The strike and dip of joints are measured in the same way as for bedding.
Map symbols for joints.

7. Description
Joints may closely resemble bedding or cleavage, especially if the joints are planar, parallel and closely spaced. It is easy to misidentify jointing as bedding in massively stratified rocks that lack the conspicuous colour and textural variations that would otherwise call attention to the attitude of stratification.

8. Description
Joints commonly display extraordinarily systematic preferred orientations. These are systematic joints.
Some joints are so irregular in form, spacing and \ or orientation that they cannot be readily combined into distinctive through going sets. These are non-systematic joints.
A joint set consists of a group of more or less parallel joints and a joint system consists of two or more joint sets of any group of joints with characteristic pattern.
systematic joint
non-systematic joint
joint set
joint system

11. joint dipping into a highway
Description
Significance:-
A knowledge of joints is important in many kinds of geological studies. The orientation and concentration of joints is very significant in engineering projects, quarry operations, etc. A large joint dipping into a highway is the site of a potential landslide.
Wells drilled in granites for water supply will be more productive in highly jointed rocks than in less jointed rocks.
Many studies of joints have been made in order to deduce the orientation of the stresses to which the rocks have been subjected.
valley
joint dipping into a highway
joint in granite

12. CLASSIFICATION
Joints may be classified either geometrically or genetically. A geometrical classification is strictly descriptive and comparatively easy to apply. but does not indicate the origin of joints. A genetic classification is more significant, but, is not readily applied in many cases.
A. Geometric Classification: Four types of joints in geometric classification.
1. Strike Joint
3. Oblique or Diagonal Joint
2. Dip Joint
4. Bedding Joint
B. Genetic Classification: Four types of joints in gentiic classification.
1. Extension Joint
3. Shear Joint
2. Release Joint
4. Tension Joint

13. CLASSIFICATION
A. Geometric Classification:
In geometric classification, the joints may be classified on the basis of their attitude relative to bedding or some similar structures in rocks that they cut.
There are four types of joints in geometric classification:
1. Strike Joint
2. Dip Joint
3. Oblique or Diagonal Joint
4. Bedding Joint

14. A. Geometric Classification:
1. Strike Joints are those that strike parallel or essentially parallel to the strike of the bedding of a sedimentary rock, the schistosity of a schist, or gneissic structure of a gneiss.
Strike joints
Dip joints
2. Dip Joints are those that strike parallel or essentially parallel to the direction in which the bedding, schistosity or gneissic structures dips.

15. A. Geometric Classification:
3. Oblique or Diagonal Joints are those striking in a direction that lies between strike and direction of dip of the associated rocks.
Oblique or Diagonal joints
Bedding joints
4. Bedding Joints are parallel to the bedding of the associated sedimentary rocks.

16. CLASSIFICATION
B. Genetic Classification:
Many joints are systematically disposed about folds and it has generally been assumed that they have resulted from the same compressive forces as those that produced the folds. In genetic classification, the joints are classified on the basis of their origin.
Genetically joints can be classified into four different types:-
1. Extension Joint
2. Release Joint
3. Shear Joint
4. Tension Joint

17. B. Genetic Classification:
1. Extension Joints are those developed perpendicular to the axes of folds and are common in orogenic belts. Such joints result from slight elongation parallel to the axes of folds.
extension joints

18. B. Genetic Classification:
2. Release Joints are those developed parallel to the axial planes of folds. It results from compression when the load is released. Release joints form at right angles to the axis of compression.
release joints

19. B. Genetic Classification:
3. Shear Joints: Two sets of joints that intersect at a high angle to form a conjugate system are often considered as shear joints, especially if they are symmetrically disposed about the strain axis or fold axis. Shear joints / fractures developed at an angle 30 degrees with the axis of compressive force.
shear joints

20. B. Genetic Classification:
4. Tension Joints result from the shrinkage of rock. The shrinkage may be due to cooling or desiccation. Igneous rocks contract on cooling. Mud and silt contract because of desiccation.
Columnar joints are tension joints found in igneous rocks and are undoubtly the result of contraction due to cooling. In columnar jointing, the country rocks is split up into a number of vertical columns which in plan view, may be square, rhombic, triangular or polygonal in outline.
section view
map view

21. CLASSIFICATION
B. Genetic Classification:
4. Tension Joints result from the shrinkage of rock. The shrinkage may be due to cooling or desiccation. Igneous rocks contract on cooling. Mud and silt contract because of desiccation.
Columnar joints are tension joints found in igneous rocks and are undoubtly the result of contraction due to cooling. In columnar jointing, the country rocks is split up into a number of vertical columns which in plan view, may be square, rhombic, triangular or polygonal in outline.

22. Left image source: http://members.aol.com/alexmx5/mammoth.htm
Right image source:

23. Left image source: http://www.vulkaner.no/v/volcan/sjordi/bcusa.html
Right image source: past/dtower/dt.htm

24. Left image source: http://users. ox. ac

25. Origin of Joints:
The ultimate cause may be several:-
a) Tectonic stresses: Causing fracturing essentially contemporaneously with the tectonic activity.
b) Residual stresses: Due to events that happened long before the fracturing.
c) Contraction: Due to shrinkage because of cooling or desiccation.
d) Surficial movements: Such as downhill movements of rocks or mountain glaciers.