1884 O Mint Marks

Don't know off the top of my head, but there are a few. Look closely for O/O, either as lines at the side or curves top or bottom.

some pics

"Round O" and "Oval O" mint marks are both known for 1884. The "fill" in the first image could be due to a number of different possibilities - all of which perk my ears up as a Morgan aficionado - but it looks like a "Round O" variety similar to your third image. They are not uncommon, but far fewer varieties exist than "Oval O's" so attribution should be relatively easy.

The second is an "Oval O," an O/O from your description, but I'm afraid I'll either have to ask for closer pics or send you to VAMworld to research things yourself:

http://www.vamworld.com/1884-O+VAMs

Well, think about the "fill" this way: The part of that mint mark which is no longer "negative" on the coin - the center - is a "positive" on the die. It sticks up on the die. It can only be "filled" if metal is allowed to flow into that area, and metal can only flow there if that "positive" is no longer attached to the die.

There are post-mint possibilities that could cause metal to flow into that area, but I can't think of any which wouldn't cause damage to the surrounding area.

I think that part of the die snapped off. It's a fascinating thought to me as a student of Morgan varieties; I don't know how much of a value-added feature it is, but it's darned cool. Me? I wouldn't liquidate that coin for love nor money.

Do me a favor. Get a similar image of the date position relative to the neck vee - get the second 8 in the date, also, if it takes another pic to do it, so we can start to try to attribute it. Hold on to the coin. Let's figure out just how interesting this coin is.