Keva

From Memory Alpha, the free Star Trek reference.

Kevas are 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")

The Star Trek Encyclopedia describes them as gemstones.