This document discusses different types of rocks and their classification. It describes three main classifications of rocks: geological, physical, and chemical. The geological classification divides rocks into igneous, sedimentary, and metamorphic based on their formation. The physical classification considers a rock's structure, dividing them into stratified, unstratified, and foliated. The chemical classification examines a rock's main chemical composition, categorizing them as siliceous, argillaceous, or calcareous. Common rock-forming minerals like feldspar, mica, and dolomite are also outlined. The document concludes by listing qualities of good building stones such as strength, appearance, durability, and describing natural beds where stones can

1. STONES
CONTENT –
1. Classification of rocks
2. Common rock forming mineral
3. Qualities of good building stone
4. Natural bed of stone

2. CLASSIFICATION OF ROCK
1. Geological classification
2. Physical classification
3. Chemical classification

3. Geological classification
In this , rocks are classified on the bases of formation
These are of three types –
1. Igneous rocks – the rocks which are formed by the cooling of magma are
known as igneous rocks.
2. Sedimentary rocks – these rocks are
Formed by the deposition of products of
weathering on pre – existing rocks .

4. 3. Metamorphic rocks – these rocks are formed by the change in character of the
pre – existing rocks.
PHYSICAL CLASSIFICATION – In this, rocks are classified on the bases of general
structure . According to this rocks are of three types
1. Stratified rocks
2. Unstratified rocks
3. Foliated rocks
Stratified rocks : these rocks possess planes of stratification or cleavage and such
rocks can easily split up along these planes. Sedimentary rocks are distinctly stratified
rocks .

5. Unstratified rocks : these rock have a crystalline granular or compact granular. The
igneous rocks of volcanic agency and sedimentary rocks affected by the movement
of earth are of this types.

6. Foliated rocks : these rocks have a tendency to be split up in definite direction only.
The foliated structure is very common in case of metamorphic rocks .

7. CHEMICAL CLASSIFICATION
This classification is known as scientific or engineering classification ,
According to this , rocks are of three types –
1. Silicious rocks : In these rocks, silica predominates. The rocks are hard and
durable. They are not easily affected by the weathering agencies.
EXAMPLES – granites, quartzites, etc.

8. 2. Argillaceous rocks : In these rocks, the argil or clay predominates. Such rocks may
be dense and compact or they may be soft . These rocks are hard and durable
but brittle. EXAMPLES – slates, laterites, etc.
3. Calcareous Rocks : In these rocks, the calcium carbonate predominates. The
durability of these rocks will depend upon the constituents present in the
surrounding atmosphere. EXAMPLES – limestone, marbles, etc.

9. COMMON ROCK FORMING MINERAL
1. Felspar –
• it is straight – splitting mineral
• It shows development of tabular crystals.
• It has usually well defined faces.
• The presence of decomposed rocks sometimes impart cloudy appearance
to this mineral.
• The rock disintegrate easily, if orthoclase is in abundance in their structure.
• The microline has deep green or flesh-red colour.

10. 2. Hornblende –
• This mineral is heavy, strong , durable but brittle.
• It’s colour is dark-green or black . It has glassy luster.
• It changes to chlorite when exposed to weather.
• It’s density is 29-30 kN/m cube and hardness is 5 to 6.
3. Mica –
• It is silcate of aluminium with potassium and occurs in thin transparent laminae or plate
• Hardness is 2 to 3
• There are two type of mica –
1. Muscovite –it has light colour and may be coloureless when available in thin layers.it density is
27.60 to 31 kN/m cube.
2. Biotite – it has dark colour and metallic lustre. It has iron content and hence when exposed to
weather , it changes to chlorite and loses elasticity. It density is 28 – 32 kN/m cube .

11. Dolomite – Its crystal are brittle.
• It is a bicarbonate of magnesium and calcium (MgCO3.CaCO3 )
• It consists 46% of MgCO3 and 54% of CaCO3.
• It is insoluble in ordinary water.
SILICA - Silica is another name for the chemical
compound silicon dioxide. Each unit of silica
includes one atom of silicon and two atoms of
oxygen.
o Pure silica is colorless, but if contaminants are present in a sample of quartz, it
may be colored.
o Silica under normal conditions of temperature and pressure is a solid, crystallized
mineral. It is relatively hard, Rating a 7.

12. QUALITIES OF GOOD BUILDING
STONE
1. CRUSHING STRENGHT : for a good structural stone , the crushing strength should be greater
than 100 N/mm².
2. APPEARANCE : the stone which are to be used for face work should be decent in appearance
and they should be capable of preserving their coloured uniformly for a long time.
o It is desirable to prefer light coloured stones as compared to dark coloured stones because there
are chances of latter variety to be attacked easily by weathering agents.
o A good building stone should be of uniform colour and free form clay holes, spots of other
colour, bands, etc.
3. DURABILITY – a good building stone should be durable. The various factors contribute to
durability of a stone are its chemical composition , texture , resistance to atmospheric ,

13. And other influences, location in structure, etc.
4. HARDNESS – the coefficient of hardness should be greater than 17 ( obtained by test ) for a
stone to be used in road work.
5. WATER ABSORPTION – for good stone , percentage absorption by weight after 24 hrs should
not exceed 0.60.
6. TOUGHNESS - Toughness of stones means it ability to resist impact forces. Building stones
should be tough enough to sustain stresses developed due to vibrations. The vibrations may
be due to the machinery mounted over them or due to the loads moving over them. The
stone aggregates used in the road constructions should be tough.
7. SPECIFIC GRAVITY - The more the specific gravity of stone, the more heavier and stronger the
stone is.
 Therefore stones having higher specific gravity values should be used for the construction of
dams, retaining walls, docks and harbors. The specific gravity of good building stone should
be greater than 2.7 .

14. NATURAL BED OF STONES
o The plane along which stones can be easily split is knows natural bed of
stones.
o Rocks have distinct plane of division along which stones can easily splits