In contrast to sleet , ice grains are largely transparent (this corresponds to the distinction between clear ice and rough ice ), in contrast to hailstones , they have no core and are not made up of layers of ice. Their size is no more than 6 millimeters.
When ice grains fall from the sky, one speaks specifically of freezing rain ; in another context, we speak of freezing rain , too, but when rain freezes on the ground, either because it meets very cold background ( Freezing rain ) or the drops themselves are hypothermic ( supercooled rain ). When grains of ice hit the ground, they too often form a solid layer of ice. In contrast to freezing rain, the ice surface is not completely smooth, but rather slightly grooved because each grain of ice forms a small hill.