hi preetam,

To get into IIT for M.Sc. after B.Sc. Geology you need to give entrance exam known as IIT JAM. You will get admission in IIT on the basis of your IIT JAM score.

Eligibility for IIT JAM :

Get at least 55% in B.Sc. for general/obc student.

Get at least 50% in B.Sc. for sc/st/obc students.

For more information regarding IIT JAM EXAM CLICK HERE

I hope this answer will help.
All the best for the future!!