Native American Stone Tool: Hand Crusher/Grinder/Miller/Pestle from MAINE

Description

Found when I was 8-9 (1980s) while diving (holding my breath, masked, diving 4-5 feet, in a lake in Livermore Maine.
Old timers growing up would always recant vague stories that the Native Americans used to use the same beach/waters that I found this one, albeit, when the water-line used to be "way over there next to that large glacial boulder near the drop-off" (aka more modern damming of the lower lake changed the water-line by 10-20 feet compared to back then...)
As-found; not changed, cleaned or altered n any way from the day it was found.
My untrained Native-American-Artifact eye still screams to me that the ergonomics of this piece scream that it was not a fluke of nature, but in fact intelligently crafted by someone a long time ago. It fits extremely comfortably in my clasped/closed fits; Lower food-to-contact-section is triangle in shape, but corners have a soft/dull rounding to them.
Measures 3 1/4" front to back; 3 1/4" W too and approximately 3 1/8" T
In briefly looking up Native American Histories on Livermore Maine, It looks like these tribes would likely have been the owner of such an artifact in the area: Sioux, or Cherokee, or Iroquois
I package well and ship out daily.