On the basis of their chemical composition engineers prefer to classify rocks as:
1. Silicious rocks
2. Argillaceous rocks
3. Calcareous rocks
(i) Silicious rocks: The major content of these rocks is silica. They are durable and hard. Examples of such rocks are trap, granite sand stones etc.
(ii) Argillaceous rocks: The major constituent of these rocks is argil for instance clay. These stones are durable and hard but they are brittle. They cannot endure shock. laterites and Slates are instance of this type of rocks.
(iii) Calcareous rocks: The major constituent of these rocks is calcium carbonate. Limestone is a calcareous rock of sedimentary origin whereas marble is a calcareous rock of metamorphic origin.