Antique Necklace

This looks like a art deco agate necklace but the clasp is reminiscent of the trombone type that I posted recently. Any idea what the age of this would be and if it’s costume?

 

Any maker's marks on it? The clasp is a tube box clasp which is still made today.

 

It looks more Art Nouveau in style to me, is it copper? Does a magnet stick?

 

From what I can see of it, the stone looks like carnelian. Same mineral as agate, just a solid color.

 

Always helpful to include a photo of the entire piece laid out. Also give approximate measurements, or put something in for scale.

Looks more 1960s/70s to me, but could be wrong. Would be helpful to see the entire piece. It has an interesting look and I like it.

No marks at all? On the back or sides?

 

The dangle looks like glass, and the bail is relatively modern. I'd say 1960s or later. The T part wants to be Art Nouveau, which jibes with the other hardware. I've seen similar clasps used on 1990s Art Nouveau Revival necklaces from those San Francisco manufacturers.

 

I agree, it is from the second half of the 20th century, my guess from the little I've seen would be 1970s-80s.
The bail is Art Deco in style, but still used. Those tube box clasps are also still used.
Could you post a photo of the stone? It could be glass, as @evelyb30 said.