So the last episode (”When It Rains”) brought up a few interesting details about Homeworld and the gem civilization that got me thinking.
First off, there’s the fact that Peridot didn’t know what rain was. Not that she’d never seen rain before, but that the entire concept of rain was entirely alien to her.
Now, rain isn’t exactly a rare phenomenon. Pretty much anywhere that has a thick enough atmosphere, it tends to rain something. Some planets rain sulfuric acid, or glass, or diamond, or ammonia, or molten steel, but the overall phenomenon of “rain” is everywhere. So it’s especially odd that it apparently doesn’t rain on Homeworld.
It may just be that Homeworld just doesn’t have that much of an atmosphere (rocks don’t have to breathe, after all), but when you couple that with more details in the episode and in other episodes, a very intriguing possibility comes up: