Nine (nava) gems (ratna) at king Vikramaditya’s court, mentioned in Kalidasa’s Jyotirvidabharana.
For the navaratna visit https://www.myindiamyglory.com/2021/01/26/historicity-of-navaratnas-of-raja-vikramaditya-kalidasa-to-vetala-bhatta/