These Mysterious Stones Found in Romania Grow, Move and Even Breed

Researchers suspect the irregular spheroid shapes were formed by the unusually long-lasting and intense seismic activity of the Middle Miocene. The shockwaves created by huge earthquakes compacted the sandy sediments and concentrated the limestone cement in spherical lumps. As the elements wore away over time, the looser sandstone around these lumps, exposing the denser trovants. (Not always though. Of the 100s of known trovants, seen across at least 20 sites through Romania, some were only unearthed after the sand around them was quarried away.)