Stones and classifications of stones

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

2. CLASSIFICATION OF ROCK Geological classification Physical classification Chemical classification

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

4. 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 Stratified rocks Unstratified rocks 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 – 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. 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. 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 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. 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. 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 – Muscovite –it has light colour and may be coloureless when available in thin layers.it density is 27.60 to 31 kN /m cube. 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. Pure silica is colorless, but if contaminants are present in a sample of quartz, it may be colored. 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 CRUSHING STRENGHT : for a good structural stone , the crushing strength should be greater than 100 N/mm². APP EARANCE : 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. I t 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. A good building stone should be of uniform colour and free form clay holes, spots of other colour, bands, etc. D URABILITY – 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. HARDNESS – the coefficient of hardness should be greater than 17 ( obtained by test ) for a stone to be used in road work. WATER ABSORPTION – for good stone , percentage absorption by weight after 24 hrs should not exceed 0.60. 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. 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 The plane along which stones can be easily split is knows natural bed of stones. Rocks have distinct plane of division along which stones can easily splits