Do you need to pay capital gains tax on such winnings (or may be some other tax). How will one declare the source.
Here's an example of it in action; arguably a pretty similar case to a precious metal falling out of the sky: https://www.forbes.com/sites/robertwood/2014/02/26/couple-fi.... Apparently the numismatists of the world have a name for this stash if you're interested: https://en.m.wikipedia.org/wiki/Saddle_Ridge_Hoard
This seems to me more like discovering a gold mine. You can't buy things with your meteorite, or divide it indefinitely into smaller pieces that keep their value pro rata. Even if it was filled with platinum ore, you'd need to smelt and refine it.
The tax treatment of treasure trove in the US is different from the treatment of discovering gold or oil: in brief, you owe taxes when you find it, instead of when you sell it or its products.
Edit: another legal question, what if you don't own the mineral rights under your own home?