Antique Lapis Lazuli Silver Earrings- European

These have an art deco feel. They are marked 870 which is an old European silver mark that is no longer used. I believe them to be lapis lazuli. They are cold to touch. There are unevenly dispersed gold coloured flecks throughout. There is no colour on rubbing with a cotton swab dipped in alcohol. However, I am not a jeweller and have no special knowledge or training in this area! They are really lovely and I have not polished or cleaned them. They have clip backs.