Gold and silver are both suitable metals for setting Green Onyx stones. Silver settings may bring out the stone's natural lustre, whereas gold can help accentuate its greenish-yellow hues. It is ultimately up to the wearer's preference for which metal to set their stone. Whichever metal you choose, it should be durable and of high quality so that it does not tarnish or scratch easily. Additionally, any setting should have prongs that securely hold the stone.