[MichaelCorleone]

-—It has been postulated that the two outer liquid giants of our solar system, Uranus and Neptune, are hiding, beneath their dense atmosphere, oceans of liquid diamond...-—

I thought diamond was either a solid or, when heated to a high enough temperature, goes straight to a gaseous state.

Guess not.

[Red Badger]

Liquid Diamond has been created on Earth, by accident.

I vaguely remember a science article from years ago, where scientists were working on something else, and were using a diamond as a base. They aimed a laser at something on the surface of the diamond, in vacuum and under high pressure. The laser was out of focus and missed the target and hit the bare diamond instead.

What they saw under a microscope was that the diamond had melted and flowed away from the spot then re-solidified.................

[Swordmaker]

I thought diamond was either a solid or, when heated to a high enough temperature, goes straight to a gaseous state.

Crystal Carbon in vacuum does indeed sublimate directly to a gas. Under very extreme pressure in a non-volatile atmosphere, it can go to a liquid carbon form. . . Which could still maintain a crystalline structure. In an oxygen atmosphere, diamond burns.