mineralization

Looking at this specimen found in the Mississippi in MN it appears to have mineralized and turned to rock. Heavy for the size, also appears it’s hollowed from what I could see through one slit in the middle. Also wondering what the black staining is?

Hello all, I was hoping to ask a few questions of someone who is familiar with the general western Mariposa County area. I ran a query for Mariposa and didn't find anything regarding ground mineralization. Hopefully I dug deep enough and am not asking the same old annoying question over again...

I have the Equinox 800 and when you manual ground balance you can get a number between -9 and 99. So I assume that a reading of lets stay 88 is highly mineralized soil and a reading of 1 or -9 is no mineralization. am I on the right track? seems the manual on page 40 says nothing about what...