Well Chuck,

First you cost me money. (The book)

Then you get me on a tear about my mystery black stone which I haven't yet 
used due to it's present state/condition.

It's obviously an old stone, not perfectly square in any direction, dings, 
scratches, corner/edge chips.
It has about a 1/8" dish on one side of the stone.
It even has some brown "splatter" on the non-dished side.
It's not been abused, nor has it been treated  lightly, it has scars.
But it's black, and it's heavy.

With a little work  I do not doubt that this could be made into a 
serviceable stone.
Up until now because of it's unknown lineage, and the fact that I have other 
stones to use it has been just sitting there waiting.

But now you made me curious enough to spend some time with it.
I do not have the equipment to cobble up a way to duplicate the procedure 
that I see on-line to do the measurement.

So I made a rough estimate the good old boy way.
I have a vernier caliper and averaged out the height, width and length 
dimension, as noted this stone is NOT square and dimensions taper .030-.040" 
everywhere.
But except for the dish all planes are reasonably straight surfaces so 
average dimensions should suffice.
I end up with about 22.713 in³ of stone which weighed 2.17# on a kitchen 
scale.

My napkin calculation puts this at a specific gravity between 2.6 and 2.7, 
and it does NOT compensate for the dish which would push it towards the 
higher side.

I'm fairly confident that this has been identified as being a BLACK HARD 
ARKANSAS, and worth some effort to make it serviceable, thanks.

-----Original Message----- 
From: Chuck Taylor
Sent: Sunday, February 12, 2017 9:53 PM
Ray,

The only book I know of about identifying sharpening stones is this one:

http://taths.org.uk/shop/69-hone

If you want to know how to identify Arkansas stones by grade, you can look 
in the archives:

https://swingleydev.com/ot/get/213402/single/

Chuck Taylor
north of Seattle