Star Trek: The Original Series, season 1, episode 25
The Devil in the Dark
Summary
Dispatched to the mining colony on Janus VI, the Enterprise is to investigate rumors of a strange, subterranean creature responsible for destruction of equipment and the deaths of 50 miners. Kirk and Spock discover a silicon-based life form, a Horta, which lives in the surrounding rock. After Kirk and Spock find the strange creature, Spock performs a mind meld, discovering the reason behind the Horta's attacks.
Summary from Wikipedia, CC BY-SA 4.0.
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