Stones of geological origins have been identified and classified as building stones which are used for different purposes. They are discussed subsequently.
2.4.1 Granite
It is a deep-seated igneous rock, hard, durable and available in different colours. It has high crushing strength and is capable of sustaining high weathering.
2.4.2 Basalt and Trap
Basalt and trap are also of igneous origin. These are effective solid rocks which have been formed on the earth’s surface in the absence of pressure by rapid cooling of the magma which also carries crystals of various minerals. These are hard, tough and durable and are available in different colours.
2.4.3 Limestone and Chalk
These are sedimentary rocks which have been formed of remnants of seaweeds and living organisms consolidated and cemented together. They are easy to work with and contain a high percentage of calcium carbonate.
2.4.4 Sandstone
This is another form of sedimentary rock formed by the action of mechanical sediments. It shows a sandy structure which is low in strength and easy to work with and dress. This is available in different colours.
2.4.5 Laterite
This is a metamorphic rock and is a sandy clayey stone. It is porous and soft. It can be cut easily into blocks and contains a high percentage of iron oxide.
2.4.6 Gneiss
It is a metamorphic rock which can be easily split into thin slabs and is easy to work on.
2.4.7 Marble
It is a metamorphic rock which can be easily cut with a saw and can be carved.
2.4.8 Slate
It is also a metamorphic rock which is black in colour and can be split easily.
2.4.9 Gravel
It is available in river beds in the form of pebbles and is of different shapes.
2.4.10 Quartzite
It is a metamorphic rock which is hard, brittle and crystalline. It is difficult to work with and is very durable.
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