The HORTA is a very rare case of
mineral intelligent race. The HORTA has been met for the first time in the pergium mines
of Janus there. The first approaches with the Horta have been rather dramatic, because the
miners came killed from a "monster that moves in the rock." . Spock understood
however of have met something of intelligent, after a mind meld with the horta.
moves through rock digging tunnels, as easily as humans walk through air. The eggs of the
Horta are silicon globes (the miners have been keeping them as souvenirs and/or destroying
them - the horta was killing the miners with her acid in self-defense to keep her species
alive (and stole the life-support system to try to make the miners go away) Every 50,000
years the race of horta all die, saving the one mother horta to take care of the eggs.
In the episode The Devil in the Dark, Kirk and Spock discuss the possibility of silicon-based beings (or beings not carbon-based) apparently forgetting that Nancy the Fotiallian salt-sucker was silicon-based. McCoy later comes down and says that silicon-based life is impossible.
Referring episode : The Devil in the Dark