This seems like an easy hardness test for a testing laboratory. In fact this seems like and easy test to see what a random selection of smart phone models demonstrate.
Anything less than a Moh 8 should not be on a smart phone. Which means the only things near you that should scratch the screen is another iPhone screen, sapphire watch face, or diamonds. I think Corning Glass makes the screen glass, so this could be Corning fault. Or, Apple light have asked for special material that is not Gorilla glass... ?