The main difference between Igneous, Sedimentary and Metamorphic rocks is the way that they are formed.
Igneous rocks are formed from a hot, molten mass of melted rock materials.
Metamorphic rocks are formed from old parent rocks undergoing intense heat and pressure.
Thus, the igneous rocks and metamorphic rocks are similar because both of these rocks are formed from high heat and pressure that deform them.
But, the major difference between them is that the metamorphic rocks do not get hot enough to melt.
