Igneous rocks: The inside portion of the earth’s surface has high temperature so as to cause fusion by heat at even ordinary pressures. The molten or pasty rocky material is known as the magma and this magma occasionally tries to come out to the earth’s surface through cracks or weak portions.
The rocks which are formed b the cooling of magma are known as the igneous rocks.
The igneous rocks are recognized in the following three classes;
(a) plutonic rocks: Such rocks are formed due to cooling of magma at a considerable death from earth’s surface. The cooling is slow and the rocks possess coarsely grained crystalline structure.
The igneous rocks commonly used in building industry are of plutonic type. The granite is the leading example of this type of rock.
(b) Hypabyssal rocks: Such rocks are formed due to cooling of magma at a relatively shallow depth from the earth’s surface. The cooling is
quick and hence these rocks possess finely grained crystalline structure. The dolerite is an example of this type of rock.
(c) Volcanic rocks: Such rocks are formed due to pouring of magma at earth’s surface. The cooling is very rapid as compared to the previous two cases. Hence these rocks are extremely fine grained in structure. They frequently contain some quantity of glass which is a non-crystalline material. The basalt is an example of this type of rock.
The rocks which are formed b the cooling of magma are known as the igneous rocks.
The igneous rocks are recognized in the following three classes;
(a) plutonic rocks: Such rocks are formed due to cooling of magma at a considerable death from earth’s surface. The cooling is slow and the rocks possess coarsely grained crystalline structure.
The igneous rocks commonly used in building industry are of plutonic type. The granite is the leading example of this type of rock.
(b) Hypabyssal rocks: Such rocks are formed due to cooling of magma at a relatively shallow depth from the earth’s surface. The cooling is
quick and hence these rocks possess finely grained crystalline structure. The dolerite is an example of this type of rock.
(c) Volcanic rocks: Such rocks are formed due to pouring of magma at earth’s surface. The cooling is very rapid as compared to the previous two cases. Hence these rocks are extremely fine grained in structure. They frequently contain some quantity of glass which is a non-crystalline material. The basalt is an example of this type of rock.
