I think the real account is in the phenomenal energy costs to convert the mines material to a final form. The glass is going to be mined as well, as even the cheap soda lime glass we see everywhere has many ingredients, and I would be surprised if the typical fiber was made of such cheap material (went and checked, and the optical fibers are likely to be doped and tuned to the application). A furnace consumes huge amounts of energy, for both refineries and glass plants (I worked at a glass plant, and the size of the natural gas line running to it 24/7 full open was shocking). Recycling helps (since the material stores some of the original energy), but there still needs to be a process to remove impurities.

As a sibling comment noted, green energy probably isn't what we would hope it to be.