Why do I keep poohing out quartzite?

A week ago I noticed that there was hard pebble like pieces in my pooh. I thought that maybe it was my diet or something. I started eating a healthy diet the past few days and it didn't change anything, the hard pebble pieces were still there. I went to the doctor with a stool sample yesterday so he could yse it. Today he told me that the hard pieces are quartzite and that it was bizarre and he couldn't figure out why it's there. Can any of ye tell me? I'm started to get freaked out cause the doctor was looking at me like I was a freak or something.