Density, Susceptibility, Resistivity, Physical property and factors of common rocks

2. Topic :Density, Susceptibility, Resistivity, Physical
property and factors of common rocks

3. Contents..
1) Density
2) Density of common Rock
3) Factors Affecting Density
4) Resistivity
5) Factors Affecting Resistivity
6) Susceptibility
7) Factors Affecting Susceptibility
8) Physical properties of common Rock

4. Density ..
The density, or more precisely, the volumetric mass
density, of a substance is its mass per unit volume.
The symbol most often used for density is ρ (the lower
case Greek letter rho), although the Latin letter D can
also be used. Mathematically, density is defined as
mass divided by volume:
ρ = m/v
where ρ is the density, m is the mass, and V is the
volume
Rock density is very sensitive to the minerals that
compose a particular rock type. Sedimentary
rocks (and granite), which are rich in quartz and
feldspar, tend to be less dense than volcanic rocks.
And if you know your igneous petrology, you'll see that
the more mafic a rock is, the greater its density

6. Low Density High Density

7. Densities of Common Rocks
 The rock densities expressed as specific gravity, which is the
density of the rock relative to the density of water. That's not
as strange as you may think, because water's density is 1
gram per cubic centimeter or 1 g/cm3. So these numbers
translate directly to g/cm3, or tonnes per cubic meter (t/m3).
As you can see, rocks of the same type can have
any Density in a range of densities, since they can contain
different proportions of minerals and voids.

8. Andesite 2.5 - 2.8
Basalt 2.8 - 3.0
Coal 1.1 - 1.4
Diabase 2.6 - 3.0
Diorite 2.8 - 3.0
Dolomite 2.8 - 2.9
Gabbro 2.7 - 3.3
Gneiss 2.6 - 2.9
Granite 2.6 - 2.7
Gypsum 2.3 - 2.8
Limestone 2.3 - 2.7
Marble 2.4 - 2.7
Mica schist 2.5 - 2.9
Peridotite 3.1 - 3.4
Quartzite 2.6 - 2.8
Rhyolite 2.4 - 2.6
Rock salt 2.5 - 2.6
Sandstone 2.2 - 2.8
Shale 2.4 - 2.8
Slate 2.7 - 2.8
Rock densities are useful to
engineers, of course. But they're
also essential for geophysicists
who must model the rocks of
the Earth's crust for
calculations of local gravity.

9. Factors Affecting Density

10. Temperature
 As the temperature of most substances increases
 Atoms move faster and spread apart.
 Expansion increases the volume which decreases the density
because the mass remains the same.
Colder Warmer

11. Example
For example, at normal atmospheric pressure, air at 0 °C has a density of ρ =1.29
kg/m3. But at 10 °C, the density of air is ρ =1.25 kg/m3, which is slightly less.
It is important to state the temperature of a material, because it is a factor in
density.

12. Pressure
 Solids
 At great depths below Earth’s
surface there is extremely high
pressure from the overlying
rocks.
 Minerals are compressed
 Volume decreases.
 Density increases

13. Fluids
(Particularly gases such as the atmosphere)
 As pressure decreases, gases expand.
 This results in an increase in volume.
 Density decreases

14. Shape and Size
 If the temperature of a material remains constant,
the size and shape will not affect it’s density.
 The mass and volume change proportionately.
Al of these Aluminum objects have the same density

15. Expanding water in pipes and cracks in rocks
will cause them to break apart

16. RESISTIVITY
Resistivity..
Electrical conductivity (or resistivity) is a bulk property of material
describing how well that material allows electric currents to flow
through it.
•Resistivity is determined by measuring the voltage required to
pass a measured amount of electrical current through the
rock.
• For a rock cube with sides of 1 m, if electrical potential of
1 V (Volt) is required for current flow of 1 A (Ampere),
then resistivity is 1 ·m (Ohm ·meter)

17. Resistivity
The measuring power of specific
method against the flow of electrical current
is known as resistivity
Unit
Ohm meter

18. Ressistivity of Range of Rocks
Range 10−5
ohm meter to 1015
ohm meter
Good Conductor
10−5
ohm meter to 10−1
ohm meter
Intermidiate Conductor 101
ohm meter t0 107
Poor Conductor 108
to 1015
ohm meter

19. TYPES
1= TRUE Resistivity
2= Apparent Resistivity

20. Factors
that will INCREASE the resistivity of a rocks
 (a) Remove pore fluid
 (b) Lower salinity of pore fluid
 (c) Compaction - less pathways for electric current flow
 (d) Lithification - block pores by deposition of minerals
 (e) Keep fluid content constant, but decrease connection between pores

21. that will DECREASE the resistivity
of a rock
 (a) Add more pore fluid
 (b) Increase the salinity of the pore fluid - more ions to conduct electricity
 (c) Fracture rock to create extra pathways for current flow
 (d) Add clay minerals
 (e) Keep fluid content constant, but improve interconnection between pores

22. Electrical resistivity of multiphase
materials
 Pure materials are rarely found in the Earth and most rocks are
a mixture of two or more
 phases (solid, liquid or gas). Thus to calculate the overall
electrical resistivity of a rock,
 we must consider the individual resistivity and then compute
the overall electrical
 resistivity. Consider a sandstone saturated with salt water. The
grains are quartzite and
 have a high resistivity (> 1000 ohm-m).
 In contrast, the pore fluid is conductive (~1 ohm-m).

23. susceptibility
In electromagnetism, the magnetic susceptibility
is one measure of the magnetic properties of a
material. The susceptibility indicates whether a
material is attracted into or repelled out of a
magnetic field, which in turn has implications for
practical applications. Quantitative measures of
the magnetic susceptibility also provide insights
into the structure of a rocks, providing insight into
bonding and energy levels.

24. Susceptibility
Definition.
The total amount of
magnetization in a substance.

25. Factors effecting
1.Temperature
 When this is high rocks tend to deform ductile and flow when this is low ( at
or near the surface)rocks tend to behave like brittle solids and fracture

26. 2. Time
When tactile forces are applied slowly over this
span . Rocks tend to display ductile behavior and
deformation by flowing and folding
3. Rock type
 Weak rock that are most likely to behave in a
ductile manner when subjected to different
stress , including rock salt, shale and lime
stone

27. Physical Properties
Luster -
This property describes the appearance of reflected light from the mineral's surface.
Nonmetallic minerals are described using the following terms: vitreous, pearly, silky,
resinous, and earthy.

28. Texture
 Definition of texture
the visual and tactile quality of
surface
 Words to use when describing the
texture of a rock.
Rough rig
Smooth soft
Bumpy hard

29. Shape
 Definition. A specific form
Words use
Round circular
Oval square
Diamond rectangle

30. Color -
Although an obvious feature, it is often unreliable to
use to determine the type of mineral.
 Color arises due to electronic transitions, often of trace
constituents, in the visible range of the EM spectrum. For
example, quartz is found in a variety of colors.
 Color of a mineral may be quite diagnostic for the
trace element and coordination number of its bonding
environment.

31. Streak -
The color of a rocks in its powdered form; obtained by rubbing the rocks against
an unglazed porcelain plate.
 Streak is usually less variable than color.
 Useful for distinguishing between rocks with metallic luster.
Weight
 definition.
 The amount or quantity oaf heaviness of rock

32.  Crystal form or habit -
The external morphology of crystals generally
reflect the internal arrangement of their constituent
atoms. This can be obscured, however, if the
mineral crystallized in an environment that did not
allow it to grow without significant interaction with
other crystals (even of the same mineral).

33. Hardness
This is the resistance of the mineral to abrasion or
scratching. This property doesn't vary greatly from
sample to sample of the same mineral, and thus is
highly diagnostic. It also is a direct reflection of the
bonding type and internal atomic arrangement. A
value is obtained by comparing the mineral to a
standard scale devised by Mohs, which is comprised
of 10 minerals ranging in hardness from talc (softest)
to diamond (hardest).

34. Mohs’ Hardness Scale