The Visitor from the Earth Core

Superboy and Krypto head underground to recover a radioactive rock that can only be found in the Earth's core. When the two discover a strange black sphere, they decide to take it back with them. Unfortunately, a strange crystalline creature follows them to the surface. When it emerges it because to wreak havoc. Eventually Superboy realizes that the black sphere is the crystalline creature's egg. They hatch the egg and take the baby to its mother. No longer angry, the mother returns to the Earth's core with her baby.