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Mineralogy: Physical Properties Of Minerals

The following are the important physical properties: i) Color ii) Streak iii) Lustre iv) Structure v) Hardness vi) Specific gravity vii) Cleavage viii) Fracture ix) Tenacity x) Form




Inorganic substances which has more or less definite atomic structure and chemical composition


It has constant physical property which are used in the identification of mineral in the field It can be divided into 2 groups


Rock forming mineral: Which are found in abundance of earth crust Ore forming minerals: which are economic valuable minerals

MINERAL GROPUS:                             


          MINERAL GROUP               EXAMPLES


          Oxides:                 Quartz, magnetite, haematite, etc

          Silicates:               Feldspar, mica, hornblende, augite, olivine,et                        

          Carbonates:                   Calcite, dolomite, etc              

          Sulphides:            Pyrites, galena, sphalerite, etc

          Sulphates:            Gypsum              

          Chlorite:               Rock salt, etc

Over 4000 mineral exist in earth crust


All are composed of oxygen, silicon, aluminium, iron, calcium, potassium, sodium and magnesium




The following are the important physical properties:


i)               Color

ii)          Streak


iii)   Lustre

iv)        Structure

v)       Hardness

vi)      Specific gravity

vii)     Cleavage

viii)    Fracture

ix)        Tenacity

x)         Form




Color is not constant in most of the minerals and commonly the color is due to stain or impurities in the minerals some minerals show peculiar phenomena connected with color.


Play of colors: It is the development of a series of prismatic colors shown by some minerals or turning about in light.


Change of colors: It is similar to play of colors that rate of change of colors on rotation is rather slow.


Iridescene: Some minerals show rainbow colors either in their interior on the surface. This is termed iridescence.




The streak, which is the color of the mineral powder, is more nearly constant than the color. The streak is determined by marking unglazed porcelain or simply by scratching it with a knife and observing the color of the powder.




It is the appearance of a fresh surface of a mineral in ordinary reflected light. The following are the important terms used to denote the lustre of

minerals. Classy or vitreous lustre    -        Lustre like a broken glass                

Metallic lustre      -        When a mineral has lustre like

metal. Pearly lustre        -        Lustre like pearls



This is a term used to denote the shape and form of minerals. The following are the important terms used to denote the structures of minerals.


Columnar Structure       -        The mineral has a thick or thin column like Structures

Bladed Structure  -        The mineral has blade like structure.

Radiated structure         -        For columnar of fibrous diverging from central Points

Lamellar structure          -        The mineral made of separable

plates. Botroidal structure                -        For an aggregate like bunch

of grapes. Reniform structure           -        For kindney shaped aggregate.




It is the resistance of mineral offers to abrasion or scratching and is measured relative to a standard scale of ten minerals known as Moh'scale sof hardness.

Hardness mineral :       Name of the


01      Talc

02      Gypsum

03      Calcite

04      Fluorite

05      Apatite

06      Orthoclase

07      Quartz

The scale comprises ten minerals arranged to order of ascending hardness; the softest is assigned a value of 1 and the hardest value of 10. Hardness of any mineral will lie in between these two limits.


Specific gravity:


It may be defined as the density of the mineral compared to the density of water and as such represents a ratio.ie specific gravity of a mineral is the ratio of its weight of an equal


volume of water. Specific gravity of a mineral depends upon the weight and spacing of its atoms.




It is defined as the tendency of a crystallized mineral to break along certain definite planes yielding more or less smooth surfaces. Cleavage is related to the internal structure of a mineral. The cleavage planes area always parallel to some faces of the crystal form typical of mineral. It is also described on the basis of perfection or the degree of easiness with which minerals can split along the cleavage planes.



The fractures of a mineral may be defined as the appearance of its broken surface. Common types of fractures are:

Conchodal fracture        -        The broken surfaces shows concentric rings Or curved surface.

Even fracture        -        When the broken surface is smooth and flat.      

Uneven fracture    -        When the mineral breaks with an irregular  Surface.  It  is  a  common fracture of many Minerals.

Splintery structure         -        When the mineral breaks with a rough.




Important properties related to tenacity of the minerals are expressed by the terms like balances, flexibility, elasticity, sectility and mellability etc. when a mineral can be cut


with a knife it is termed 'sectile'and if the slice cut out from it can be flattened under a hammer. It is also said ella'mble''brittle'minerals. Term elastic is used if it regains its

former shape as the pressure is released.


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