It looks like Roman glass…from Crete. I have admired Roman glass made into jewellery for a long time. One of my daughters recently visited Crete and brought back this piece, after many strenuous hours in the hot sun, and bending over with her nose poised a few centimetres above the sand. She brought back, in a plastic bag, a lot of seawater and some sea glass. Most of the glass ended up in the recycle sea glass bottle. But there were a few bits worth keeping. Thank you Emma and Katerina.