Is there a difference between un collar and una gargantilla?
I'm guessing that "collar" is any necklace but "gargantilla" is a chocker (close to the throat???
2 Answers
Well I believe you have answered your own question. It's the same as a necklace and a choker in English, one loose, one tight.

From the R.A.E "gargantilla":
f. Adorno femenino que rodea el cuello.
f. Cada una de las cuentas que se pueden ensartar para formar un collar.
Therefore it would appear that "collar" and "gargantilla" could be used.