Igenous Rock classification

Igneous rocks show a wide variation in mineral composition and texture due to conditions of crystallization. The most useful classification is based on mineralogy and texture.

Relative silica content – presence of quartz indicates excess of silica and felspathoids indicate deficiency of it.

Igneous Rocks

Igneous rocks are formed by cooling and solidification of magma.

  90% of the earth crust is composed of igneous rock.

  SiO₂ (40% - 75%), Al₂O₃ (10% - 20%) and oxides of Ca, Mg & Fe
less than 10%.

  Acid magma is rich in Si, Na & K.

  Basics magma is rich in Ca, Mg & Fe.

  Based on the silica percentage present in the rocks, they are classified into four.