Hello Rudra! To know what qualification and eligibility criteria you need to be a gemologist, you should first know what gemologist is. 

WHAT IS GEMOLOGIST? 

Gemologist are people who keenly studies the physical and chemical bonds of a gemstones and check its authenticity. The increasing use of gems in the commercial markets has took the identification, evaluation and processing of gemstones to a most demanding line these days. This course will help the candidate to handle and process the gems also identify gems, grade and assort  to designing those gems.
Gemologist understand the science and chemistry behind gemstones and examine their underlying physical properties and bonds. They check the gemstones are real or fake and provide a Jewell or a goldsmith with an idea about how much pressure they should give on that gemstones so they will not be broken with their keen detail oriented, near vision and analytical skills.

Qualifications to be a gemologist

• To become a gemologist you need to study B. Sc in gemology or B. Des in jewellery design. One of these course will help you to become a gemologist or other job option related to a gemologist. Candidates can have diploma in jewellery design or gemology too. 
• To study B. Sc in gemology you need to complete your 12th in science stream. And to study B. Des in jewellery design you need to complete you 10+2 examination from a recognized board in India. That means in both course you need to qualify 12th examination. 

Eligibility criteria for gemologist

• Students must appear in entrance exams for their preferred college. Exams such as-

National Institute of Fashion Technology (NIFT) Entrance Exam, Graduate Aptitude Test in Engineering (GATE), Aligarh Muslim University Entrance Examination, National Institute of Design Aptitude Test (NID DAT), GD Goenka Design Aptitude Test (GD Goenka DAT)

• To study masters courses to become a gemologist, you need to complete the graduation degree with at least 55 percent marks from any recognized Institute or university. And have to sit for entrance exam if there any.
• The candidate should at least be 18 years and above to study gemology. There is no upper age limit.

Hope all these information will help you!