Alumina Saturation Index

Feldspars are the abundant minerals that occurs in igneous rocks, and alumina is one of the most important element in the feldspars. Thus alumina saturation is based on weather there is an excess or lack of Al to make up the feldspars –

• Orthoclase = 1/2 K₂O, 1/2 Al₂O₃
• Albite = 1/2 Na₂O, 1/2 Al₂O₃
• Anorthite = 1CaO, 1Al₂O₃

Based on the relative amount of K₂O, Na₂O, CaO and Al₂O₃ the rocks can be divided into three groups –

1. Peraluminous rocks :- These rocks have more Al₂O₃ than combined K₂O, Na₂O, CaO.
   • The alumina rich minerals will be present like Muscovite, Corundom, Topaz, Kyanite, Sillimanite, Andalusite.
   • They will have corundom in NORM and no diopside.

REFERENCES :-

• google images