Did I Just Join The Gold Club?

[Chase Goldman]

First of all it looks like gold, get it tested.

FWIW, brackish water has LESS salinity than seawater, not more.  It is where tidal freshwater and seawater bodies  mix.  Regardless, salt will not corrode gold like that.

Farm runoff should have no effect on gold corrosion either.

As someone previously mentioned, it looks more like heat damage, not chemical pitting.  So therein lies the mystery... provided it tests out as pure gold vs. a gold plated medallion or non-gold item.

[F350Platinum]

Ok some specs:

It's almost exactly the same size as a dime, It's about 0.0385 thick, it weighs 1 gram or .03 ounce. It rings when dropped on a table.

I'm saying if it quacks like a duck it's probably the copper core of a modern dime. What keeps it so shiny is still a mystery, could be that it's kept polished by the sand.

I'll have it tested, but it's probably copper.

Had to leave something behind that ID'd at 25 behind when the tide came in, it was under a large piece of piling on its side. I didn't want to pry the log up with my sand scoop.

Went out in the field afterwards and had a good day there, musket ball, old dog tag, 5 buttons. One button is silverplated, 3 tombac, and one that says "Double plated London" on the back. We're looking at a bad week ahead so I made the most of it.

[GB_Amateur]

Excellent sleuthing!

A year ago this most recent Thanksgiving weekend I searched a friend's small fish pond.  At the pond's outlet I got a high TID and pulled out a thin copper slug.  I was hopeful it was a large cent (about the right size) but when my friend noticed the edge was reeded the hope faded.  In fact it was exactly what you said -- the copper core of a clad quarter.  You can read what I wrote here on the site.  My hypothesis was that the acid from decaying leaves had eaten off the Cu-Ni clad layers.

You took the right approach -- holding hope that it was valuable but being open minded enough to research until you got a convincing determination.  The opposite (from the start assuming it was worthless) will never result in a great discovery. 

There's a much more satisfying and profitable ending that occurred a couple years ago where a person found (apparently in a rummage sale box although I don't think that was ever confirmed) what appeared to be an extremely rare $5 gold piece.  He showed it to some coin dealers and all told him it was a fake.  He didn't give up but instead sent it to a professional grading service which authenticated it.  He then sold it through a rare coin auction house and it fetched over $2 million.

[oneguy]

I've dug 7-10 burnt silver dimes and 1 silver quarter that'd been thru a fire. Some come out full sized with blisters and pitting...some come out almost paper thin, especially on the edges and some bent.  One thing they all had was pitting and blisters exactly like your "coin".  My bet is gold coin that's been thru a fire.....

[F350Platinum]

5 minutes ago, oneguy said:

My bet is gold coin that's been thru a fire.....

And therein lies the oddity.

I got together a 1916 copper wheat penny, a modern dime, the "coin", and my 3 ounce 14k white gold wedding ring.  I ID'd them all:

Wheat penny was a solid 20, dime a solid 25, my wedding ring a 15, and this "coin" came in at 14/15. 🤔 

I guess only an assay will tell for sure.

[F350Platinum]

Another test:

The silver Half Real I found last week is .0395, only slightly thicker (.0385) and it weighs .04 ounce vs. .03. It is nearly the same size. Copper density is 8.96g per cubic centimeter, and silver is 10.49. Gold is 19.32g/cc, it would weigh almost twice as much.  It's copper. 

[Dances With Doves]

If that is a gold coin that is the ugliest   one i ever  did see but it could have been in a fire.It would still put you in the gold coin club if it's gold.

[oneguy]

Sure looks like gold in the pic?  You're the boss and if you say it's copper then it's copper!  If it were mine and it looks in real life like it does in the pics I'd take it to your local coin dealer or jeweler and have them do a quick acid test on it....but that's me?

[GB_Amateur]

11 hours ago, F350Platinum said:

Wheat penny was a solid 20, dime a solid 25, my wedding ring a 15, and this "coin" came in at 14/15.

My copper core (only) USA quarter still ID'd at 30 on the ML Equinox, same as an undamaged clad quarter.  You probably saw that I determined the weight of the core and compared to the weight of my specimen.  (I think it was still off by 20-30%.)  Did you do that?

X-Ray Fluorescence Spectroscopy (XRFS) would solve the mystery.  I've many times wished I had one of those hand-held units, but can't justify the cost for what effectively would be a toy for me.  Coin dealers, pawn shops, and others who buy precious metals often have them.

[kac]

Good old acid test should help too, not like you're going to lose any detail.

Could very well be a copper alloy coin.