Chemical diagram for cummingtonite? Any suggestions on diagramming the chemical structure for cummingtonite? 
$$\ce{(Mg,Fe)_7 Si_8 O_{22} (OH)_2}$$
As I understand it, the $\ce{(Mg,Fe)_7}$ says the molecule has seven atoms that could be either Magnesium or Iron, with probably more Magnesium than Iron, meaning the structure isn't precisely defined, i.e. a mineral not a specific molecule.  Is there a suitable way to diagram this that looks nice but not excessively complex? 

In fact, I'm rather ignorant about chemistry, but started screen printing subtlety goofy neck ties.  I'm envisioning doing essentially this but vertically and adding a chemical structure diagram.  I'll do the final pattern in latex if possible.

p.s.  If I were making ties professionally, maybe I'd diagram an assortment of different cummingtonite molecules as a background for the formula.  I'm not doing that, way beyond my screen printing ability.  Just curious though, how does one know the probability distribution for the Magnesium and Iron?  Just varies by sample perhaps?
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)