They may be classified in the following four ways.
Stones are classified as per the classification if their parent rocks.
Geological classification: Igneous rocks, sedimentary rocks, metamorphic rocks.
Physical classification: Stratified rocks, unstratified rocks laminated rocks.
Chemical classification: Siliceous rocks argillaceous rocks, calcareous rocks.
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Igneous rocks are formed from cooling of molten lava material erupted from the interior of the earth. These are solid, massive and crystalline stones without stratification. e.g. basalt, granite dolerite.
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Sedimentary rocks are formed by denudation and deposition of existing rocks because of the weathering action of water wind, frost, etc. the consolidation of these deposited layers takes place under pressure by heat or by chemical agents as natural cement. e.g. sandstone limestone, gravel
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Metamorphic rocks are originally either igneous or sedimentary rocks that have undergone considerable changes in their constitution, i.e. in their shape, structure and sometimes, even in their mineral composition, under the influenced of the agents of metamorphism.e.g. marble gneiss slate, schist etc.
Stratified rocks
These rocks show a layered structure in their natural environment. They possess planes of stratification or cleavage and can be easily spilled from sedimentary.
Unstratified rocks
Rocks which do not strata and cannot be easily split into thin slabs fall into this category. e.g. marble, granite, trap etc.
Siliceous rocks
These rocks have silica as their main component. They are hard durable and not easily affected by weathering agents. e.g sand, granite etc.
Argillaceous rocks
These rocks have clay or alumina as their main component. Although these rocks are dense, compact and hard, they are brittle and cannot withstand shock. e.g slate, laterite etc.
Calcareous rocks
These rocks have calcium carbonate as their main constituent. The durability of these rocks depends upon the atmospheric constituents as they are upon by hydrochloric acids. e.g. marble, limestone etc.
