Anas bin Maalik Radiyallahu 'Anhu says that the ring of Rasulullah Sallallahu 'Alayhi Wasallam was ,made of silver and the gem stone was from Abyssinia (RU)
English reference (RU): Book 11, Hadith 82 (RU)
Arabic reference (RU): Book 12, Hadith 87 (RU)