Associated with strength and stability, the mineral bodies of the Rock type provide them with armor and encourage brute strength. Unsurprisingly a number of "naturally artifical" species can be found here, but it's also commonly noted that the revival of fossil pokemon also binds minerals to their cellular structure, boosting their already prodigious strength to incredible degrees. Most rocktypes fall into either 'sculpture' or 'armor' forms, being either mobile mineral forms that cannot breed normally, or "wearing" their rocks as natural armor. Very few Rock Types are actually pure Rock, mostly due to the difficulty in naturally forming sapient minerals, and even some of those that are are fossil type or, in the case of Regirock, possibly manmade.
With their strength and armor, Rock type pokemon may well be forces of nature for how easily they can brush through opposition. In the phsyical realm they are powerhouses, able to smash through trees and shrug off blows that could damage buildings. The sheer weight of their muscle can squash bug types, cripple flyers, shatter ice, and pound fire into the ground. Normal and Poison types struggle to get through their natural armor, flying tipes bounce off half the time, and fire type attacks wash around their stoney flesh.
However, brute strength does has its drawbacks. In a ranged environment Rock types tend to be sitting ducks. They struggle to land a hit on the mobile and precise Fighting types, who meanwhile hit their pressure points quite thoroughly. Ground and Steel types simply have more power from either pushing through the dirt or wearing metal, being able to "bully the bullies" as it were. Water and Grass types especially ruin the Rock type's armor, using their power to seep into the crevices and break apart the very thing that Rock Types love most. Consequently, rock types like barren areas.
Rock types almost exclusively have their namesake mineral deposits on the outer surface of their body, if they are not actually comprised of minerals themselves. They tend to be burly, thickset, and covered in browns and greys.
Rocks. With very little exception, rock types eat rocks.
The majority of Rock Types actually need outside assistance to breed, and must be cloned using a Ditto.