Kevas were commonly traded goods among merchants during the 23rd and 24th centuries. Spock posed as a trader of kevas and trillium while on Organia. Arne Darvin did the same while aboard the USS Defiant. (TOS: "Errand of Mercy" ; DS9: "Trials and Tribble-ations") In the first draft script of TOS: "The City on the Edge of Forever" , keva was established as a kind of Vulcan food which contained purple juice. The Star Trek Encyclopedia (4th ed., vol. 1, p. 414) described them as gemstones.