The mixtures of pure substances are quite common in nature. Some mixtures are homogeneous others are heterogeneous. The atmospheric air is a homogeneous gaseous mixture of nitrogen, oxygen and other gases in smaller proportions. Oil is a natural mixture of hydrocarbons. The rocks, like granite, are solid heterogeneous mixtures. The homogeneous mixtures have uniform physical aspect and consists of a single thermodynamic phase. The heterogeneous mixtures, on the other hand, are formed by an aggregate of thermodynamic phase in coexistence. Due to gravity, the different phases of a heterogeneous liquid mixture are arranged one above the other, separated by menisci and sorted according to density. In a heterogeneous solid mixture the phases are displayed in a fragmented and intricate arrangement.