Stone ID

[russhi]

This stone appears to be sedimentary.
It measures 15/16" x 2" x 8"
It produces a grey slurry
It is very hard and has a lot of grit like a coticule
Holding it to the light and looking down it, it is polished like glass where I started to flatten it.
The discolor in the stone are stains. It is pretty the lighter color you see in the stone which is a light grayish beige with very faint yellow veins.
My dmt 325 will do it slowly. I think I going to flatten it on glass with silicon carbide. Any help will be appreciated