Read about the Archimede's principle at: http://en.wikipedia.org/wiki/Archimedes%27_principle#Archimedes.27_principle.
There was a heavy stone mantelpiece above the fireplace. An ornate mantelpiece was sometimes used for gas heaters in residential dens.
14lbs = 1 stone
62.8kg is equivalent to 9.90 stone.
11 kg is approximately 1.73 stone.
1 stone is 14lb (fourteen pounds) or 6.35Kg.
12.2 stone is 77.47kg
tungsten
6 stone
15 stone
12 stone
10 stone
Because they are heavy