> You can use a germanium diode or even Shottky now instead of a “crystal”.

Or a razor blade or a piece of roofing lead and a needle.

Now I’m interested…

Diodes occur naturally, all you need to do is find them!

Good places to look for them are conductors and crystals.

https://en.wikipedia.org/wiki/Crystal_detector

https://rimstar.org/science_electronics_projects/razor_blade...

Good luck! And don't sneeze once you've found a good spot.