A Crime Against Science

Captain Kirk and Spock encounter a creature which looks like an animated clump of partially molten stone. The creature threatens them and receives a direct phaser blast. Injured, it escapes by burrowing quickly through solid rock. Spock examines a piece of the creature knocked off by the phaser and determines that it is indeed silicon-based, and that it secretes a strong acid which allows it to move through rock as easily as humanoids move through air. Spock's tricorder readings show that there is only one creature within a hundred miles. As it is the last of its type, killing it would be a crime against science.