Iron sinks in water because it is denser than water. The density of iron is about 7.87 g/cm^3, while the density of water is 1 g/cm^3. This difference in density causes iron to sink when placed in water.
Which rock? Any liquid that is dense enough will support a rock; the most common would likely be mercury, in which even iron floats.
It is quite common for various things to float in water. But any liquid can cause things to float.
Solid iron will float in liquid Mercury. In most liquids it will sink.
-- The density of iron near room temperature is around 7.9 gm/cc, whereas at the same temperature, mercury is liquid with a density around 13.5 gm/cc. A lump of iron will float nicely in a bowl of mercury at room temperature. -- Don't forget that aircraft carriers and battleships are also pieces of iron, and that they float nicely in water.
It is not just the weight matter in floatation or sinking.The shape,surface area or the base liquid that matters.For eg. a very flat sheat of iron weighing 85gm will float in water but a bead(ball )of iron weighing 85gm will sink.On the other hand an iron bead of 85gm will float in mercury.
Any object will float if it has less density than the liquid.
Gold can float on water if there's a layer of oil on the surface. To break the surface tension, a drop of Dawn soap will do the trick.
Anything that doesn't float in water is less dense than water, say iron? So if you drop an iron bar into a glass of water, you can say that the iron sinks or you can interpret it as the water floats? If you are referring to liquid, then mercury.
One way would be to find a liquid that is chemically inert to both metals and has a density between that of iron and that of aluminium. In such a liquid, the aluminium would float and the iron would sink.
The liquid with a lower density float over the liquid with a highrer density.
An object will float on water if it has less density than the water. Or than any other liquid on which it is supposed to float.