The home planet of the Halkans, a people of absolute pacifism who refuse the Federation mining rights to their dilithium in the original series episode Mirror, Mirror.
The Halkan homeworld is rich in dilithium crystals. In Mirror, Mirror, Kirk negotiates with the Halkan Council, led by Tharn, for the right to mine them. The Halkans decline, since they cannot be sure the Federation will always be peaceful and will not allow their crystals to power even one death.
An ion storm over the planet disrupts the transporter as the landing party leaves and exchanges Kirk, McCoy, Scott and Uhura with their counterparts from a parallel universe.
There the ISS Enterprise has orders to destroy the Halkans if they refuse the Terran Empire. Kirk stalls the attack as long as he can and, before returning home, urges the mirror Spock to spare them and to change the Empire.