What episode centers on a silicon-based lifeform killing miners on Janus VI?

“What episode centers on a silicon-based lifeform killing miners on Janus VI?” The answer is “The Devil in the Dark.” The episode first aired on March 9, 1967, during the first season of Star Trek: The Original Series.

The Enterprise responds to an emergency at a pergium-mining colony on Janus VI, where an unknown creature has killed workers and damaged equipment with a corrosive substance. Kirk initially treats the creature as a dangerous monster, while Spock suspects that it may represent an entirely unfamiliar form of life.

The investigation reveals the Horta, a silicon-based organism that tunnels through rock and protects thousands of silicon nodules—its species’ eggs. Spock’s mind meld establishes that the Horta attacked because miners had destroyed its offspring. McCoy then saves the wounded creature with silicon-based cement, transforming the crisis into a first-contact story.

The common mix-up is “The Man Trap,” which also features a creature killing humans, but its salt-draining alien is unrelated to Janus VI or silicon-based life.