MAGNETIC PROPERTIES OF ROCK

Actually i have been trying to put this article together for awhile now,because i know some people who aren't geologist won't believe that a rock can also have a magnetic property, i think this a detail article to help them to know about it . So am writing about the magnetic properties of rock.

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We are all surrounded by rocks,as i remember clearly my first year in studying geology,it is known that rocks are natural occurring solid that contains two or more elements which build them up and are all elevated above the sea level. Their are different rock types that exist naturally.

Igneous rocks( Gabbro)

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characteristics of igneous rocks

1. They are hard in nature
2. They are crystalline in nature
3. They do not contain fossils
4. They have zero porosity
5. They are formed by the solidifation and cooling of magma
6. Examples of igneous rocks are granite,gabbro e.t.c

Metamorphic rocks(Serpentinite)

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characteristics of metamorphic rock

1. They are classified based on their texture and composition
2. They rarely have fossils present in them
3. Presence of bands on the rock
4. They can react with acid
5. Foliation is present
6. Examples of metamorphic rocks are quartite,gneiss e.t.c

Sedimentary rocks

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characteristics of sedimentary rocks

1. They have pore space in them
2. Presence of fossils
3. Foliation is not present
4. Example of sedimentary rocks are shale,sandstone e.t.c

All this different rock types are formed by different processes,igneous rock are formed when magma cools down on the surface of the earth or beneath,it can form extrusive or intrusive igneous rock,examples of igneous rocks are granite,diorite e.t.c. Metamorphic rocks are formed from pre existing rocks,when they undergoe heat and pressure while sedimentary rocks are formed from sediments which are been transported by agents of denudations and deposited in a basin which accumulates together to form sedimentary rocks.
A rock contain two or more minerals in their definite proportion,therefore magnetic properties of rock can be defined in the presence of ferromagnetic and ferrimagnetic minerals.

DIFFERENCE BETWEEN FERROMAGNETIC AND FERRIMAGNETIC

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Ferromagnetism and ferrimagnetism are each varieties of magnetism, the familiar force that draws or repels positive metals and magnetized objects. The variations among this arise at microscopic scales and are seldom mentioned outdoor a lecture room or technological expertise laboratory. Ferromagnets and ferrimagnets are both exceptionally sturdy as compared to one of a kind forms of magnets, and that they have achieved considerable roles in human information.

SUSCEPTIBILITY OF ROCKS AND MINERALS

what is magnetic susceptibility of rocks?

Magnetic susceptibilty measures the magnetic properties in a rock,it refers to the ability of a rock to attract or repel out of magnetic field.

PARAMAGNETIC AND DIAMAGNETIC

If the magnetic susceptibilty of a material is greater than ZERO,the material is said to be paramagnetic because the the degree of magnetization is greater than the empty space,whereas it is diamagnetic when the MS is less than ZERO.

This simply means where their is no external field i.e the rock sample has zero net field

The susceptablitlites of various rocks and minerals

Material------------- Susceptibility x 10-3 (SI)
Air--------------------- about 0
Quartz---------------- -0.01
Rock Salt----------------- -0.01
Calcite-------------- -0.001 - 0.01
Sphalerite------------- 0.4
Pyrite------------- 0.05 - 5
Hematite------------ 0.5 - 35
Illmenite------------- 300 - 3500
Magnetite------------ 1200 - 19,200
Limestones--------------- 0 - 3
Sandstones------------- 0 - 20
Shales------------ 0.01 - 15
Schist------------ 0.3 - 3
Gneiss ------------- 0.1 - 25
Slate---------------- 0 - 35
Granite---------- 0 - 50
Gabbro------------ 1 - 90
Basalt------------- 0.2 - 175
Peridotite ------------- 90 - 200
One of the property of rocks is magnetic susceptibility,which is used during magnetic exploration.
The basic and ultrabasic rocks have high magnetic susceptibility,metamorphic and igneous rocks has low values of of magnetic susceptibility,whereas sedimentary rocks have a very small magnetic properties in general.
In as much as metamorphic rocks has low values of magnetics susceptibility,they depend upon their parent materials which they are made of.
For example,Metapsammites and metapelites they both have different magnetic susceptibility compared to each other.
Magnetic susceptibilty in rocks depends on the magnetic grain alignment and the shapes distributed throughout the rock in study.

MAGNETIC FABRICS

Magnetic fabrics is the variation of magnetic properties as a function of the orientation and shape of minerals grains in rocks which provide a good explanation to the physical compositions of or loose sediments. which helps to interprets the physical processes that affect the rocks.

HOW TO MEASURE THE SUSCEPTIBILITIES OF ROCKS

Magnetic susceptibilities can be measured with a hand held susceptibility meter called KAPPAMETER, compact cassetteor the sample can be returned to the laboratory where it can be analysed accurately;

Diagram of a kappameter and compact cassette

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The SM-30 Magnetic Susceptibility Meter

SM-30 Magnetic susceptiblity meter is a pocket sized meter which has a very high sensitivity which enable a geologist on a field to measure a sediments or rocks which have a very low magnetic susceptibility. Therefore we can measure the magnetic susceptibility of quartz,limestone, or water.

Description of SM-30 magnetic susceptibility meter

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1. it has 3 push buttons which controls it
2. it has a beeper which gives the intervals in which informations are picked from the rocks in study.
3. The SM-susceptibility meter is programmed to off automatically if no button is pressed for 3 minutes.
4. The interesting part is that it uses an element called lithium for it battery.
5. it is able to store 120 readings.
6. it has a PC connectivity.

REFERENCES:

1. https://www.eoas.ubc.ca/courses/eosc350/content/foundations/properties/magsuscept.htm, geophysical foundation
2. fabrics
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3. Rock Physics and Phase Relations: An AGU online reference, © by the American Geophysical Union, 1995.

Blakely, R.J. , Potential Theory in Gravity and Magnetic Applications, Cambridge University Press 1995.

Breiner, S, 1973, Applications manual for portable magnetiometers , published by Geometrics.

1. Reynolds,J.M (1997), An introduction to applied and environmental geophysic

2. http://www.geoafrica.co.za/reddog/kappameter/magsusc.htm,the susceptibilty meter.

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