Can glass such as marbles hold any magick energy? I know it's not the same as a natural stone so I was wondering. Also, is it harder to enchant something that isn't of a natural material in general?
Everything holds energy. I don't think its harder to put my energy in something unnatural. I've put my energy into crystals as well as plastic items. It works fine for me.
Also remember this, glass is just melted sand. Silica to be exact. Silica is a naturally occurring mineral usually found in quartz. Glass is more of a natural element than most people realize