Search:

Trick of the light, the dots on mine are definitely black.

I was thinking TOS myself, I haven't seen anything else that looks similar so far, the slurry is very pale milky white, I tried it out on a new scalpel blade, 50 odd laps on the flat of the blade...

It originally came from a dental laboratory and was used to touch up scalpels, it's quite small 4"x1" and the surface is extremely hard and glassy.
90146
A closeup of the surface
90148
Clues...