Each material is located in a separate layer/group (in Blender 2.79) or collection (in Blender 2.8+). the Blender 2.79 file contains materials for Cycles, and the Blender 2.8 file contains materials for both Cycles and Eevee.

Materials are applied to both a simple plane and a cylinder within the files, for anyone who may wish to have a base mesh to start working from.

If you want, you can play around with the .blend files themselves (you can move the camera around, add your own HDRI, hit render, etc), but I advise saving a backup of the original file first before doing so.

For general use in your projects, I recommend appending the data you wish to use into a new scene. This can be done by appending materials, groups/collections, or objects.

The shaders for both Eevee and Cycles 2.8 materials are identical, but I've given them separate names to avoid any confusion while working. The models within the Cycles .blend scene use adaptive subdivision to displace the mesh, whereas the models in the Eevee scene use the displacement modifier to do this. If you need extra displacement detail in the Eevee scene, you can increase the level of the subdivision modifier (by default, I've set it to 2).

When rendering with Eevee, I would rely on the normal map to provide the smaller details when the subdivision modifier is set to lower values. If you decide to set the subdivision higher (for example, to 4-6), I recommend doing a test render with and without the normal map enabled in the shader. I've found that at higher subdivision levels, the normal map creates unnatural shading on the model. All example renders shown here for Eevee had their normal maps disabled, since I was using (typically) 6 levels of subdivision. Something to keep in mind.

I also didn't bother rendering with the AO maps enabled, but I know some people like having them, so they're included in the shader as well. Popular blending modes for AO maps seem to be "overlay", "soft light" and "multiply".