My Daughter Found This Collecting Shells On The Maine Coast - Any Thoughts?

1) I agree, but if given the choice I am taking a coin to a coin shop for an opinion/appraisal. Also, none of us know if the OP has a coin shop nearby.
2) The two main coin shops I frequent in town both have the tools to check if this is silver without doing a scratch test. They do enough volume in bullion/scrap and with bullion prices where they are (plus with so many fakes), it's a small investment for them to make and a necessary tool to protect their businesses.
3) Coin shops see it all and deal in all beyond just bullion/Morgans/proof sets. I would trust them to either have the knowledge or connections to more accurately determine the authenticity and value of this coin over a jeweler or pawn shop. Would you take a piece of jewelry to a coin shop hoping to get an appraisal beyond the scrap value? Let's say he takes it to a jeweler or pawn shop and they determine it is silver. Ok great, what if he wants to get an estimate of its value? Why make two stops when a coin shop can do both?

Thank you for the links...I am almost certain it is
2 Reales - Phillip II. The images and weight are correct.

https://en.numista.com/catalogue/pieces61948.html

I would say that together with the COA, it's priceless!

With a COA like that I dont think anybody can deny its authenticity. Frame it up with the coa and it will be priceless.

Priceless.

For easy reference comparison, here are the two sides rotated properly and pasted side-by-side:


This is Potosi mint (Bolivia) - almost certainly Philip III, 1610s or so.

To the eyes of someone who has a good amount of experience with cobs (salvaged AND not) and has gotten pretty decent at recognizing casting mushiness/porosity vs. environmentally-caused mushiness/porosity... the surface of the piece is very questionable. I wouldn't categorically condemn it from these pics alone, but the detail overall is just too "mushy" (again, even accounting for water-caused erosion). In addition, there are numerous "discrete" stand-alone pores, even on the reverse which displays better detail with less "seawear". That is a telltale sign on cast cobs.

The other thing which MAY be an issue, from what can be made out from the photos and the given weight of approx. 7 grams, is WHAT DENOMINATION it's supposed to be. At that weight, a genuine piece could only be a 2 Reales or possibly a 4 Reales. Weights as made for this era of Potosi were pretty consistent right around 6.85g as made for a 2R and 13.7g for a 4R. Even if the scale is rounding to the whole gram or maybe even slightly "off"... if this piece is a genuine 2R, I would expect a weight really no higher than possibly as much as 5.5g. If it were a genuine 4R with this amount of loss to the elements, I expect a weight in the 9-10g range, not as low as 7-8g.

The denomination mark is blobbishly visible to the right of the shield. It first appears could be Roman "II" as 2R... however, there looks to be a "o" over that mark which would appear only on a 4R, not 2R (o over IIII... due to Spanish "cuatro" ending in o).

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PS - to this point:


I have read probably a dozen forum threads over the years where people posted "cobs" they seemingly truthfully found, metal detected, etc. on beaches - and they were known or obvious replicas. Basically, some people get their jollies by messing with around with the treasure hunter/metal detectorist types so they get all excited about their "treasure" and then eventually get told it's not. It's unfortunate, but it is a known thing.

Regardless of whether it's genuine or not, if it was me I'd do like JakesCoins suggested - frame the "COA" and the coin together as a keepsake. Even if it's a replica, that's a great story and something to treasure!

Oh, and by the way,