Antique Diamond Stick Pin

Description

You are bidding on an old diamond stick pin.
This pin was either my dad's or his dad's.  Were it my dad's, it would have been worn as early as in the 1920s; my grandfather's, still earlier.  In either case, it can be classified as an antique.
I'd guess the diamond's setting, the star motif, is brass; the pin itself is anyone's guess (silver, steel, ?).