Mineral is a naturally occuring inorganic solid with a definite chemical composition and physical structure. Common minerals include quartz, feldspar, mica, amphibole, olivine, and calcite.
There are approximately 4000 different minerals, and each of those minerals has a unique set of physical properties. These include: color, hardness, diaphaneity, specific gravity, cleavage, fracture, magnetism, solubility, and many more. These physical properties are useful for identifying minerals. However, they are much more important in determining the potential industrial uses of the mineral.
In this post, we’ll discuss about some of the major physical properties of minerals
A. Physical Properties of Minerals depending upon light:
Color:
The color of a mineral depends upon either the selective absorption of light or the reflection of light within the body of minerals. Color variation due to chemical impurities. E.g. Azurite –Blue, Malachite –Green, Pyrite –Yellow, Hematite –Gray.
Streak:
It is the color of a mineral when it is finely powdered. It can be determined by rubbing the minerals on the piece of unglazed white Porcelain plate i.e. Streak plate. E.g. Haematite – Cherry Red.
Luster :
It is the appearance of a mineral surface in reflected light. On the basis of variation in the nature of the reflecting surface, luster can be divided into the following categories:
• Metallic luster: The shining surface to that of broken piece of metal. E.g. gold
• Non-metallic luster: The shining surface to that of non-metal. The non-metallic luster is as given below.
I. Adamantine: The luster of brilliant glossy i.e. Diamond. E.g. Corundum
II. Vitreous: The luster of broken glass. E.g. Quartz, Topaz
III. Resinous: luster of yellow resin. E.g. Sphalerite
IV. Greasy: The luster of an oily glass. E.g. Nepheline
V. Pearly: The luster of the pearl. E.g. Talc, Brucite
VI. Silky: The fibrous feature found in minerals like silk. E.g. Asbestos
Degree of Intensity of Luster:
- Splendent: The reflecting surface with brilliancy and giving well-defined image e.g.Hematite.
- Shining: The surface is producing an image due to reflection but giving an undefined image. E.g. Celestite
- Glistening: The mineral is affording a general reflection from the surface without an image. E.g. Talc
- Glimmering: The mineral affording imperfect reflection only from the points over the surface. E.g. Flint, Chalcedony
- Dull: The total absence of luster in minerals. E.g. Chalk, Kaolin
Transparency:
It is the ability of minerals to transmit light. The varying degree of transparency is given below.
• Transparent: Light passes through the mineral and the outline of an object can be seen clearly. E.g. Halite, Calcite
• Translucent: Light passes through the mineral but an object cannot be seen through it. E.g. Chalcedony
• Opaque: No light passes through the minerals. E.g. Galena, Pyrite
B. Physical Properties of Minerals Depending Upon Cohesion & Elasticity:
Hardness:
- The hardness of a mineral is its resistance to scratching or abrasion. In 1824 German Mineralogists Friedrich Mohs selected a set of minerals in order of increasing hardness i.e. 1 to 10 in number on the basis of the test. Such scale of hardness is known as Mohs Hardness Scale.
- Talc- Mg3Si4O10(OH)2
- Gypsum- CaSO4.2H2O
- Calcite- CaCO3
- Fluorite- CaF2
- Apatite- Ca5F(PO4)3 or Ca5Cl(PO4)3
- Orthoclase- KAlSi3O8
- Quartz- SiO2
- Topaz- Al2F2SiO4 or Al2SiO4(OH)2
- Corundum- Al2O3
- Diamond- C
Some other possible hardness test can be done by using the following common objects.
Fingernail about- 2.5
Copper coin 2.5 – 3
Glass 5–5.5
Knife Blade 5.5–6
Steel File 6.5–7
Cleavage:
It is the ability of a mineral to break along a certain plane within a specific direction. The following parameters are used to evaluate the quality of cleavage.
- Perfect Cleavage: Mineral breaks into very thin sheets with mirror-like surfaces. E.g. Mica, Gypsum.
- Good Cleavage: The mineral break in a definite direction to form a smooth surface. E.g. Calcite, Galena, Halite.
- Distinct Cleavage: Mineral broken with a rough irregular surface. E.g. Feldspar, Hornblende.
- Indistinct Cleavage: Mineral broken with the undulated surface. E.g. Beryl, Apatite.
- Non-Cleavage: No broken plane in a definite direction. The cleavage can be observed in sets i.e. I, II, III, etc.
Fracture:
It is the breaking down of the mineral mass in a direction other than cleavage direction. They are not parallel to each other. Fracture is defined by using the following terminology.
- Conchoidal: The fracture having a smooth and curved surface. E.g. the surface developed on a piece of broken glass.
- Even: The fracture having a more or less smooth and plane surface.
- Uneven: The fracture having a rough surface.
- Hackly: The irregular fracture with sharp elevations.
- Splintery: The mineral separates out into fibers. E.g. Asbestos
- Earthy: Like the appearance of hard clay.
Parting:
The mineral split fairly from the weakness plane. The weakness plane produced by deformation, inclusion, etc.
Tenacity:
The measurement of mineral deformation or disintegration under outer
force i.e. hammering. The tenacity can be defined as the given below.
- Brittle: When parts of mineral separates in powder form. E.g. Calcite
- Sectile: Mineral cuts without powder. E.g. Gypsum, Graphite
- Malleable: Mineral flattens out under a hammer. E.g. Gold
- Flexible: Mineral bends without breaking when the force is removed. E.g. Talc
- Elastic: When the mineral attains its previous position after the withdrawal of the force. E.g. Micas
C. Physical Properties of Minerals Depending Upon Density Compared With That Of Water:
Specific Gravity:
It is the ratio of the weight of a given volume of mineral to the weight of an equal volume of water. Specific Gravity can be determined by the chemical balance, Jolly’s spring balance, or Specific Gravity Bottles.
The weight of mineral in air = W1
The weight of mineral in water = W2
The weight of an equal volume of water = W1-W2
Specific Gravity = W1/ (W1-W2)
D. Others Characteristics of Minerals
Habit (Form):
98% of the minerals are crystalline & a few are amorphous. The major habits are as given below.
- Crystalline: Minerals have recognizable crystal forms.
- Massive: Minerals have no recognizable crystal forms.
Taste:
Example: Halite (Rock salt)
Odor (Smell):
Example: Pyrite gives strong smell in heating.
Feel:
Smooth or greasy. Example: Talc
Magnetic:
Example: Haematite
