Here follows a short summary of how to append the materials into your own scenes:

1. Open your scene.
2. Go to File > Append (or Link).
3. Navigate to the Granites.blend file.
4. Click on the blend file to view its contents.
5. Navigate to the NodeTree folder and select the Granite_... node groups to load the shaders.

For the complete documentation on linking and appending, view the Blender documentation: Blender Appending And Linking.