Question 658550
I assume you meant "a stone in the form of a sphere..."

The formula for the volume of a sphere is:
{{{v = (4/3)*pi*r^3}}}
{{{r = d/2 = 42/2 = 21 cm}}}
{{{v = (4/3)*pi*(21^3)}}}
{{{v = 12348*pi = 38792.4}}} cubic centimeters.  At 2 grams/cc, the stone would weigh 77584.8 grams, or 77.5848 kilograms