A Vulcan gong
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)
For "Amok Time", Douglas Grindstaff was involved in creating the sound of the gong, which he described as "Chinese-type." He recalled, "We got on the scoring stage and recorded a nice gong, then we turned it around and recorded twangs on the electric guitar, and combined everything to give the gong a distinctive quality." (The Star Trek Interview Book, p. 237)
Production illustrator Andrew Probert once characterized the design for the long range shuttle as having "subtle repetitions of that ceremonial 'gong' shape." [1]