How to export .mtl files for 3D textured objects

I would really like to deploy my textured 3D graphics in the web with sketchfab in my blog. Unfortunately, Mathematica only exports the shape of the 3d graphics, i.e. the .obj file, but omits the associated material file (.mtl) which is not generated.

Is there any way to accomplish my aim and deploy from Mathematica textured-graphics to sketchfab or any other standard textured material format? Perhaps someone has written a basic .mtl exporter?