Unfortunately, the real-world environment is naturally endowed with some grit that clocks in pretty high on the Mohs' scale. Just bog-standard "sand" can get up

Unfortunately, the real-world environment is naturally endowed with some grit that clocks in pretty high on the Mohs' scale. Just bog-standard "sand" can get up to 7 and it's not hard to find little bits of grit that go even higher, made either of pulverized naturally-hard materials or industrial stuff. A quick Google suggests titanium is a 6, which in addition to being scratchable by pretty much all the grit, makes it significant lower than most cell phone screens now. It's going to be hard to keep the sheen on those for any length of time.