Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
It is Haram for a man to wear a chain around his neck even if it not made of gold, since this action constitutes an imitation of women in their special characteristics.
The Prophetic Hadith: "The Prophet (Sallallahu Alaihi wa Sallam) cursed males imitating females and females imitating males" [Reported by Imam Bukhari].
Allah knows best.