This is a Trifari choker length necklace from the 1950s - 1960s (like many Trifari necklaces during the 1950's and 1960's used hook clasps, and because these were narrow, they do not include the crown symbol). It is made of Trifanium (Trifari's patented "goldplating"). It is very similar to their "Whirlwind" set, which was made in 1957.
It measures 16.5" from the ball end to the hook end of the closure (where the Trifari mark is stamped).
Here's a handy-dandy reference to Trifari Maker's marks: