Gliese 581 d is probably too massive to be made only of rocky material.

Triton's density implies it is probably about 30-45% water ice, with the remainder being rocky material.

Titan is primarily composed of water ice and rocky material.

Furthermore, the planet is most likely composed of rocky materials.

The two dwarves appear to have similar densities, consistent with them being primarily made from rocky material.

This can be also inferred by the presence of metals in the rocky material making up the disk.

That means the rocky material is much like the moon and the rock that makes up the Earth.

In great contrast to its ice, our comet's rocky material had formed under white-hot conditions.

A planet is assumed to form out of the rocky material and gas left in an orbiting disk around a new star.

This would explain the dearth of rocky material within the rings.