In the late 1960s, Superman and Lois Lane encountered a race of Lava Men that were spawned in lava that was released from a volcano near a small village in Mexico. It started with just one Lava Man, until Superman punched it, causing it to break into small pieces and then those pieces formed into other Lava Men. Superman used water to return them to their natural non-living state, allowing them to return to the form of lava.
It was his hope to burn everything and make the surface just as hot as it is in the molten center of the Earth. But he and his army are stopped by Super Friends members Superman, Aquaman and Wonder Woman.
Details of the Lava Men
The Lava Men's physiology was fairly simple to describe, they were inorganic silicon-based life forms, made of living lava. The original group of Lava Men encountered by Superman appear to have no connection to the second group, and may even be a separate species altogether, as they were not humanoid shape until they were spawned from the lava on the surface. This isn't to say that they might take on a humanoid appearance only on the surface, but there's not enough data to tell for sure. The original group encountered started from just one Lava Man, and from him spawned several others, all of which were returned to their natural state. This group had the ability to communicate verbally, through some unknown gibberish sounding language. They appeared to at least have close to human-level intelligence, and they were quite hostile.
The second group encountered in Ocean City appeared that they may have even been more intelligent than the first group of Lava Men. They were capable of speech that could be understood by humans. They didn't appear to be able to spawn other Lava Men from their bodies, but this isn't known, since none of them were ever punched in such a manner. They were soldiers serving in a monarchy, which their king, Solderath was the leader of. Superman was able to defeat this group of Lava Men by using his heat vision, which was apparently a very dry heat, which caused them to harden.