Vokaya was a turquoise-colored mineral unique to Vulcan which emitted a harmless but distinctive radiation.

In the alternate reality, Spock gifted a Vulcan amulet made of vokaya, once owned by his Human mother Amanda Grayson, to Nyota Uhura. Its radiation proved useful in locating Uhura (and therefore all the surviving captured members of the Enterprise's crew) when she was held captive by Krall on the planet Altamid in 2263.

Upon learning of the mineral's unique quality, Leonard McCoy opined that Spock had given his girlfriend a "tracking device", something the Vulcan never intended. Later, during Captain James T. Kirk's thirtieth birthday party at Starbase Yorktown, McCoy eyed the amulet uncomfortably, knowing its true nature. Upon Spock's pleading with his eyes for McCoy not to tell her, he let it go. (Star Trek Beyond)