What falls but never breaks, and breaks but never falls?

I’m stolen gold or slang for cheeks, one found in chests, the other in seats.

I sit on a throne with a crown on my head, or I stay on your desk with your pencils instead.

Not from sun, yet still I gleam, a quiet night’s reflected beam.

If you use me in moderation, you’ll feel fine; if you use me every day, I’ll do you harm and leave you with lasting effects.