Multiple studies demonstrate that the extreme high-pressure and high-temperature conditions inside ice giants like Uranus and Neptune facilitate the chemical demixing of hydrocarbons, leading to diamond precipitation (often referred to as diamond rain).
The retrieved literature contains specific thermodynamic and shock-compression studies (e.g., [0], [6]) showing that diamond precipitation is thermodynamically favorable and experimentally reproducible under the extreme interior conditions of ice giant planets such as Uranus and Neptune.