Without any markings jewelry is impossible to date accurately !! Jewelry did not necessarily follow a style such as furniture or clothing did !! But I have seen similarly made rings and I would say this one dates to approx. 1920`s art nouveau era !! That was a very nice thing for your friend to do !! Its not an expensive ring but will be a treasured keepsake I am sure !!
It belonged to my friend, who is 60+ years old. She’s had it since she was small. It was given to her by her Grandmother. We don’t know how long her Grandmother had it but it went through “friends” Mother also. At any rate, I always love this ring on my friend and always said I want it “heired” to me. One day, not long ago, she came to spend the weekend with me and pulled it out of her pocket and said, “I decided I want you to have this BEFORE I die so I can see you enjoy it! I have been it’s new owner for about a year now.