Can You Solve this Ice Diamond Riddle? ft. Vsauce’s Michael Stevens

it depends on the size of the ice cube and the mass of the diamond; if the diamond is heavy enough to make the ice cube sink and the cube is small, when it melts the water level will decrease as water in ice form has a greater volume than in liquid forms will be displacing more water before than after, however, if the diamond is small and the ice cube is big and floats, then when it melts the volume of water from the ice will just add to the volume of water, making the level rise as the diamond was not heavy enough to pull the cube down and displace a large amount of water