Silicon nodules
These hatch into young soft Horta that exude digestive acid uncontrollably until thier first armor forms, fairly quickly.
The Horta species possesses (as compared to carbon-based lifeforms) an unusually long life-cycle. Every 50,000 years, all of the Horta die out except for one, the so-called mother Horta, who then watches the eggs until they hatch and mothers and protects them. Horta eggs are spherical in shape, and they seem to mostly consist of silicon, aside from a few trace elements. They are stored in the Vault of Tomorrow in the Chamber of the Ages.
The Vault of Tomorrow (also the Altar of Tomorrow) is located in the Chamber of the Ages on level 23 of the Janus VI colony. This vault is where millions of Horta eggs are stored and watched by the mother Horta. In 2267, miners of the colony inadvertently destroyed thousands of eggs when opening up level 23, causing the mother to go on a murderous rampage throughout the colony. (TOS: "The Devil in the Dark")
