[_yb2s]

I believe you, but there is some other explanation here- it warrants further investigation. You can scrape a regular glass window (about MOHS 6.5) clean with a razor blade (about MOHS 6.0) and it is impossible to scratch it, just from that tiny difference in hardness. I do this all the time, e.g. recently to get paint that my kid painted on the house windows off.

Your brass keys should only be about 3.0, and gorilla glass a 9.0- you should be able to rub keys into brass dust all day long and not mark the screen.

I store my keys right in my pocket with my glass iPhone SE, and it doesn't have a mark on it.

I suppose it is possible you have keys with some weird material or coating, or as another poster suggested- maybe something like an abrasive dust got stuck on your key.

[kuschku]

Brass? Who said anything about brass?

Typical keys are made from nickel plated hardened steel and nickelsilver. Considering the shiny coating is long gone and the keys are ferromagnetic, I assume it's the first. The keys are certainly hard enough to scrape my glass ceramic stove.

And reports online say that gorilla glass victus is the mist scratch prone gorilla glass, scratching at or around 6 already :/

[ralphhughes]

I think you may be onto something here. Taking apart old machinery I have often observed that the hardened part of a shaft is worn and has a noticable groove detectable with a fingernail. However the part that rubbed on it is often much, much softer eg a rubber oil seal. My theory is that the much softer material is so soft that microscopic inclusions of something much harder (grit?) are caught in the material and then abrade the harder shaft. Something similar may be occurring in the keys on glass case?

[drjasonharrison]

Cutting with a lubricant and grit is super effective. Silicon dioxide, that is sand, is everywhere.