I see yellow coti's that sometimes have a brownish look to them (not tile) on one side that kinda looks almost purplish and I wonder if thats what this is. This stone is pretty smooth and mounted on something very coarse but it has very little specs of white all through it. It makes quite a slurry when I run it on 400 grit paper and water.It reminds me of a very hard piece of chalk. This piece is broken on one end but measures 2x4.5 inches on the shortest side and its 7/8" thick. Could someone help me identify it please? I am new to this. Thanks very much. Scott