Ukonvasara or Ukonkirves is the symbol and magical weapon of the Finnish thunder god Ukko, and was similar to Thor's Mjolnir. Ukonvasara means hammer of Ukko and ukonkirves means axe of Ukko. With Ukonvasara, Ukko created lightning. Pagan Finns sometimes carry hammer or axe-pendants on their necks like the Christians sometimes carry a cross.
Ukko's hammer was probably originally the same thing as the boat-shaped stone axe. While stone tools were abandoned with the advent of metalworking, the origins of stone-weapons became a mystery. Stone axes, so called thunderstones (called Ukonvaaja in Finnish), were found on ground especially after big rain that removed some dirt. They were believed to be weapons of Ukko, stone-heads of striking lightnings. Shamans collected and held stone-axes because they were believed to hold the power to heal and to damage.