Unmarked Filigree Pin

I found this pin among the “cheap stuff” in a second hand store. It has the old c clasp and the same construction as a pin I posted a few months ago. The design is different, however. The other pin has a coral in the centre but this one has a black stone. I don’t think this it is an onyx because it looks rather very dark grey and feels lighter.
Although it is not marked I think it might be sterling.

Thanks for looking:)