You also have to consider the production of both materials as well. You also have to consider e-waste which is rarely ever recycled for some reason. Anyway for the process of making glass (which I know little about correct me If I'm wrong) you need a specific type of sand which comes from riverbeds. Its needed due to it's very round nature which happens from water erosion. Obviously making either glass or plastic is not good for the environment. but we also have to consider how apple fixes the back glass. There are lots of variables I hadn't thought much about until now.
This is a nightmare in every sense of the word.