Limestone: These are sedimentary rocks composed mainly of calcium carbonate. They show great variation in their properties and, therefore, not all types are useful as building stones. They can be used as road metal for the construction of floors, stairs, walls, etc. Limestone is also used for the manufacture of cement and lime. The use of limestone as a facing stone should be avoided in areas where the air is polluted by industrial gases or in coastal areas where sea breezes may attack them.
Marble: These are metamorphic rocks and have been formed from limestone under high temperatures. Marbles vary greatly in colour, structure and texture and most of them are suitable both as an ornamental stone and as a construction material.
Basalt and Trap: These are also igneous rocks and are generally heavier and darker than granites and also stronger, but may contain cavities and pores within them. They are extensively used for rubble masonry, foundation work and road construction.
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