It has now been confirmed with greater confidence that it rains diamonds on Neptune and Uranus, and that diamonds accumulate into vast diamond-floating icebergs at some depth.
These giant planets have some methane in their atmospheres. Because of lightning, methane transforms into graphite, which falls as droplets deeper down. At a certain depth, the pressure is so high that graphite rain transforms into diamond rain.
The new research subjected diamond to pressures higher than those at Neptune and Uranus and confirmed the theory that liquid carbon is denser than solid diamond. Previously, computer simulations suggested this, but we could only speculate.
It means that, similar to water ice floating on oceans and forming icebergs on Earth, diamond rain should reach liquid carbon at some depth on these huge planets. It likely then accumulates into diamond icebergs and platforms. It must look spectacular if we could illuminate it and reach it with cameras. It will be immensely difficult, probably impossible, to construct devices that could reach such depths on Neptune or Uranus, survive, and send back footage for us to see.