Stone materials for Cycles
This is a collection of rock materials for the Cycles engine in Blender. I have tried to reproduce the look of a variety of real rock types. They are quite detailed and are best used at close-up range.
Slope and altitude based materials in Cycles
If you've used any graphics program that specializes in landscape generation, such as Terragen, you have probably seen that a core feature is the ability to automatically calculate the borders between snow, barren stone and grass from the geometry. Snow is only possible above a certain altitude where the temperature is below the freezing point, and even there snow will not stick on surfaces that slope too steeply. Similarly, grass will only be found below a certain altitude where it's warm enough, and will also not grow on too steeply sloping ground.