Chemical diagram for cummingtonite?
Crystalline structures of inorganic materials aren't usually represented by diagrams, but rather by 3D renderings. First, you need to find a crystallographic structure file, which are usually in CIF format. A Google search leads to this one for cummingtonite.

Then, you need some molecular visualization software. Here, I use CrystalMaker, which can create nice photorealistic 3D images, and has a simple tool to record animations. The result is here:



($\ce{Fe}$ is pink, $\ce{Mg}$ is yellow, $\ce{Si}$ is blue; both $\ce{Mg}$ and $\ce{Si}$ are at the center of the tetrahedra, and oxygen atoms correspond to all the tetrahedra edges)