Green diamonds were a type of gemstone, coveted for their beauty. Every known green diamond was immature by geological standards causing them to be radioactive.
Prince Xizor was a known collector of green diamonds, giving them to his mistresses who began to wear on him. After the end of these flings, Xizor would dispatch a messenger to deliver the beautiful stone to any of the woman who refused to leave him alone. As his mistresses would open the gift box, they would grab the stone and die immediately, after which a protected agent would recover it.