The Vulcan gong was an ancient Vulcan musical instrument. It was hexagonal in shape, made of an unknown metal, and struck with a hammer that was partially made from a green stone.
During a Vulcan wedding ceremony, it was customary for the groom to call the wedding party by striking the Vulcan gong. (TOS: "Amok Time")
One gong was at T'Les' residence on Vulcan in 2154. (ENT: "Home")
A similar gong was rung during Spock's fal-tor-pan ceremony on Mount Seleya in 2285. (Star Trek III: The Search for Spock)