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.

Silicate Structure

Nesosilicates  (Island Silicates)  

Oxygens atoms are not shared with other SiO₄^-4 tetrahedrons. Ratio between Si & O is 1:4. The basic structural unit is SiO₄^-4. Eg. Olivine and Garnet group (Mg,Fe)₂SiO₄.

The atomic structure of nesosilicates are generally dense which cause the mineral of this group to have high specific gravity and hardness. Crystal system is generally equidimensional and have poor cleavage.

Interview question

Commonly Asked (& Tricky) Interview Questions

Be Prepared for these!!!

v        Tell me about yourself.

v        What are your greatest strengths?  

v        What is your greatest weakness?                     

Pumices and Scoria

                                     
Pumice /ˈpʌmɨs/, called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles and thicker vesicle walls and being dark colored and denser.