To my knowledge,
Superannuation is a contract between an employer and an employee . When the period of service mentioned is over , you say that on account of superannuation he left the company.
Gratuity : This is payment made to an employee for his continuous service of 5years. He will be payed certain amount which will be calculated based on his/her basic pay X No. of years of service X 15/26 .
Anyway pl cross check the same.
From India, Madras