I’ll give you 25¢ for the coin.
I have been collecting indian stone tools and portable rock art for years. I to have found two rocks that are carved into snake/turtle heads. Although not as detailed as yours.I wish i could get some info on them. I also have so many other native rocks that i would love to know more about. If theres anyone interested in seeing pics and has knowledge on indian rocks please let me know. Thanks
Given that the OP is still active, how about an update?
do NOT bleach it or clean it. i’d suggest bringing it to local museum … or, better yet, contact archeological curator.
Well it appears like the eyes are anthropomorthised… made human looking…
If you decide that is the case, its an asian thing to do… the previous owner was chinese tradition, perhaps born in the year of the snake.
I dont think there is much to it. perhaps look to see if there are any tool markings. Looks dremel carved to me… like a small hand held cutter with a tiny cutting wheel …
Based on the last two replies, I thought I post a notice that this thread is originally from 2012.
The OP has been active recently.
Thus my noting it in post 43:
https://boards.straightdope.com/sdmb/showpost.php?p=21226402&postcount=46
Ahhh, ninja’d, sorry
But he can only type with the rattle at the end of his tail.
Well, I laughed at that.
I wonder what Shag would have done with it?
Oh wow, I haven’t thought about this for years until this thread got resurrected. I’ll send an email to the person whose gravel it was found in and ask if he ever pursued the mystery further.
Well, bummer. I thought for sure you had a made a mint and bought a small island, with, alas, no wifi. Living it up in the south seas. All the while, we schmucks are up here slogging through our pitiful lives, somehow. 
You say that like they’re still alive.
I just read a Jules de Grandin short story by Seabury Quinn about a guy who collects Druid artifacts and becomes possessed by a Druid priest and tries to kill people.
Just sayin’.