This is "Gemini" - one of the star signs. Made by Ferro & Lazzarini at Murano. These star sign weights were in regular production from, at least, 1977 to, at least, the early 1990s.
Anyone know if these are still being made - bearing in mind that the glass production of that company is now only continiued by the new company Eugenio Ferro (
see here)?