The following are important building stone, their composition, properties and uses:
1. Granite:
It is an igneous rock. It is mainly composed of quartz, felspar and mica. Its specific gravity is 2.64 and compressive strength varies from 70 to 130 MN/m2. Its colour depends upon that of felspar which may be brown, grey, green and pink. A fine grained granite offers high resistance to weathering. It can be easily polished and worked. It is used for exterior facing of buildings.
2. Slate:
It is an argillaceous rock. It is mainly composed of alumina mixed with sand or carbonate of lime. Its specific gravity is 2.8 and compressive strength varies from 60 to 70 MN/m2. It has grey or dark blue colour. A good slate is hard, tough and fine grained. It is suitable for use in cistern. The slate in the form of tiles is used as an excellent roof covering material.
3. Gneiss:
It is a silicious rock. It is mainly composed of quartz and felspar. It is more easily worked than granite. It is a good material for street paving.
4. Sandstone:
It is a sedimentary rock of silicious variety. It is mainly composed of quartz, lime and silica. Its specific gravity is 2.65 to 2.95 and compressive strength varies from 35 to 40 MN/m2. Its usual colours are white, grey, brown, pink etc. The fine grained stones are strong and durable. It is suitable for ashlar work, mouldings, carving etc.
5. Limestone:
It is a sedimentary rock of calcarious variety. Its specific gravity is 2.6. It is available in brown, yellow and dark grey colours. It is used in large quantities in blast furnaces. It may be used as stone masonry for wall.
6. Marble:
It is a metamorphic rock of calcarious variety. Its specific gravity is 2.7 and is available in many colours. It is very hard and takes a fine polish. It is used for carving and decoration work.
7. Kankar:
It is very impure lime stone containing 30% of alumina and silica. The hard kankar is used for foundations of buildings.
8. Laterite:
It is a sandy clay stone containing high percentage of iron oxides. It has a porous and cellular structure. Its specific gravity, varies from 2 to 2.2. The laterite blocks are suitable as building stones whereas nodular laterite proves a very good road metal.
9. Moorum:
It is a decomposed laterite and has deep brown or red colour. It is used in surfacing fancy paths and garden walks.
10. Quartzite:
It is a silicious sand stone which has been subjected to metamorphic action. It is strong and durable. It is used as a road metal or railway ballast or in concrete.
