These amulets belong to European tradition from immemorial time.
It was believed that these stones were the remains of lightnings fallen down on the world and they were considered magical. They became objects from apotropaic and sacred values, propitiatory of luck and highly protective against lightning. The stones of thunder could be embedded in the foundations of houses or walled inside of them. In ancient Rome the wedge-shaped stones found in the fields were called cerauniae, and they were deemed closely related to lightnings. This superstition was handed on through the centuries: in the Middle Ages the lightning stones were mounted in silver jewels on which were often engraved figures of crosses or other symbols. Even in the eighteenth century, and until the early twentieth century, the farmers who found the stones guarded them as a talisman in the house.
These stones were merely tools smoothed by prehistoric man.