Joints form when rock fractures due to stresses exceeding its brittle strength. They typically occur in sets of parallel fractures. Joints are classified by their formation process, such as sheeting joints which form as lava cools, or by their geometry, such as bedding joints which are parallel to stratification. Factors like bed thickness and lithology influence the spacing between joints. Joints are important in fields like engineering and hydrology, as they can impact rock strength and allow fluid flow.

2. CONTENTS:
• JOINTS
• FORMATION
• TYPES w.r.t FORMATION
• TYPES w.r.t GEOMETRY
• SPACING b/w JOINTS
• IMPORTANCE

3. JOINTS:
 Joint is a fracture in rock where the
displacement associated with the opening of
the fracture is greater than the displacement
due to lateral movement in the plane of the
fracture (up, down or sideways) of one side
relative to the other.
 There is little to no lateral movement across
joints.
 Joints generally occur as sets, with each set
consisting of joints sub-parallel to each other.

4.  Fractures in general can also be described as
self-similar, or having a fractal geometry.
 If many fractures occur in the same area and
have a similar orientation, they are referred to as
a set of fractures. Individual extension fractures
are referred to as joints, and a group of them is
called a joint set.

5. FORMATION:
 Joints form in solid, hard rock that is stretched
such that its brittle strength is exceeded (the
point at which it breaks).
 The rock fractures in a plane parallel to the
maximum principal stress and perpendicular
to the minimum principal stress (the direction
in which the rock is being stretched).
 This leads to the development of a single sub-
parallel joint set.

6.  Continued deformation may lead to development of
one or more additional joint sets.
 The presence of the first set strongly affects the stress
orientation in the rock layer, often causing
subsequent sets to form at a high angle to the first
set.
 Joint sets are commonly observed to have relatively
constant spacing, which is roughly proportional to
the thickness of the layer.

7. TYPES OF JOINTS:
 Joints are classified by the processes
responsible for their formation, or their
geometry.

8. TYPES WITH RESPECT TO
FORMATION:
 Joints are classified into following types on
basis of formation:
 Sheeting joints
 Tectonic joints
 Unloading joints (Release joints)
 Exfoliation joints
 Cooling joints
 Master joints

9. SHEETING JOINTS:
 When magma cools fast, cooling is done towards country
rocks and size of material become courser at center due
to slow cooling and cause shrinkage of layers.
 These joints are more or less parallel to the surfaces of
ground.

10. TECTONIC JOINTS:
 Tectonic joints are formed during
deformation episodes whenever the
differential stress is high enough to induce
tensile failure of the rock.
 They will often form at the same time as
faults.
 Measurement of tectonic joint patterns can
be useful in analyzing the tectonic history of
an area because they give information on
stress orientations at the time of formation.

11. UNLOADING JOINTS (RELEASE JOINTS):
 Joints are most commonly formed when uplift and erosion removes
the overlying rocks thereby reducing the compressive load and
allowing the rock to expand laterally.
 Joints related to uplift and erosional unloading have orientations
reflecting the principal stresses during the uplift. Care needs to be
taken when attempting to understand past tectonic stresses to
discriminate, if possible, between tectonic and unloading joints.

12. EXFOLIATION JOINTS:
 Exfoliation joints may be a special case of unloading joints formed
at, and parallel to, the current land surface in rocks of high
compressive strength, although there is as yet no general
agreement on a general theory of how they form.

13. COOLING JOINTS:
 Joints can also form via cooling of hot
rock masses, particularly lava,
forming cooling joints, most
commonly expressed as vertical
columnar jointing.
 The joint formation associated with
cooling is typically polygonal
because the cooling introduces
stresses that are isotropic in the plane
of the layer.

14. MASTER JOINTS:
 Meters of long joints having splay joints are know
as “Master Joints”.
 These joints may be open, closed or may be
filled with secondary minerals.
 Behavior of these joints depends upon
mineralogy; if rocks is fine grained , Joints
surface morphology will be smooth and if rocks
is course grained , Joints surface morphology will
be rough.
 These Joints helps us to develop secondary
porosity and help in oil accumulation.

15. TYPES WITH RESPECT TO ATTITUDE
AND GEOMETRY:
 Joints can be classified into three groups depending
on their geometrical relationship with the country
rock:
 Bedding joints
 Strike joints
 Dip joints
 Oblique joints
 Cross joints

16. BEDDING JOINTS:
 Bedding joints are parallel to the bedding plane having
same dip and strike.

17. STRIKE JOINTS:
 Joints which run parallel to the direction
of strike of country rocks are called
"strike joints"

18. DIP JOINTS:
 Joints which run parallel to the direction of
dip of country rocks are called "dip joints"

19. OBLIQUE JOINTS:
 Joints which run oblique to the dip and strike
directions of the country rocks are called "oblique
joints".

20. CROSS JOINTS:
 These joints are formed perpendicular to the fold axis.
They are formed as the result of compression.

21. SPACING BETWEEN JOINTS:
 Average distance between joint surfaces; dependent
upon:
 Bed thickness : Joints closely spaced in thinner beds.
 Lithology : Stiffer lithology's then closer spacing.
Less stiff rocks then wide joint spacing.
 Tensile strength of the rock : Lower tensile strength then
more joints.
 Magnitude of extensional strain.

22. IMPORTANCE:
 In geotechnical engineering a joint forms a discontinuity
that may have a large influence on the mechanical
behavior (strength, deformation, etc.) of soil and rock
masses in, for example, tunnel, foundation, or slope
construction.
 It is long been recognized that joints (fractures) play a
major role in the subsurface fluid flow of water in aquifers
and petroleum in oil fields. Major industry research projects
have been dedicated during the last decades to the study
of faulted and fractured reservoirs.

23. REFERENCE:
 http://en.wikipedia.org/wiki/Joint_(geology)
 http://simple.wikipedia.org/wiki/Joint_(geology)
 http://www.infoplease.com/encyclopedia/science
/joint-geology.html
 http://maps.unomaha.edu/maher/GEOL3300/wee
k1/joints.html
 http://www.britannica.com/EBchecked/topic/3055
97/joint
 http://geology.about.com/library/bl/images/bljointi
ng.htm
 http://education.yahoo.com/reference/encyclope
dia/entry/joint-geo