This a classic box chain necklace from Miriam Haskell. It appears to have been gold gilt or plating over brass but much of the gold has worn away.  There is an overall darkened patina with slightly brighter gold in the background.  The box links have a lined, textured design with the clasp signed Haskell.  There is also the oval Miriam Haskell hangtag.  Measures about 30 inches long so you can wear it as is, add a pendant or double for a choker.  The width is 3.5mm.

Simple yet elegant!