Can I Sell A Diamond I Found In My Apartment? (usa)

I found a diamond earring in my apartment that looks to have been hiding (extremely well) for at least 5 years. I've been living in the apartment for almost a year and a half. Is it illegal for me to keep it? (I'm also torn on whether or not it's immoral, but that might be a different subreddit)

Full context/story:

I was looking for spare shaving cream in our guest bathroom and just opening and closing all the drawers, somewhat firmly. When I closed the top drawer, I heard something clunk. I opened the next drawer down and sure enough, tucked in the very back, there was an earring.

It was in very rough shape. There was green all around the silver which made the gem look green. It was generally dirty and dusty. I didn't think much of it at first but after looking at it closely for a while, I decided to rinse it off with some dish soap and water. It started to look more like it could be real... The main thing that made me doubt it was the size of it. It's probably about 4x the size of what I could afford for my wife's engagement ring working as a bartender. Comically large, to us at least.

I followed some instructions off of the internet to clean it further - once it was totally clean it shone incredibly bright. I bought a tester off of Amazon and it seems to be real. What are my legal options here?

Turning it into the police for them to ultimately never find the owner and me to be out a lot of money seems pointless. But if that's the law, I'll do it. I assume there's a grey area because I found it in my apartment rather than on a public beach or something, but I really don't know.

If it's just immoral to keep it I could try and track down the owners.. I know the first and last name of the previous tenant since we still get their mail sometimes. My hangups there are 1: that feels almost creepy 2: what if it wasn't theirs either and they just say yes anyway? 3: from a moral standpoint, do I really need to try to return a big diamond earring to someone who clearly is well off and likely collected insurance money for this earring, when my wife and I were, the day I found the diamond, talking about picking up second jobs over the summer? (Issue here: if it was passed down as a family heirloom, I'd feel really bad).

Really would love feedback here. TIA!