You're in unique company since I believe there are only a handful of members that have Hindostan stones.

I'm also glad to hear that you find them to be fine grit stones. The turn of the century Arkansas Geological Survey mentions Hindostan IIRC but did not give the stone extremely high marks for honing fine edged instruments. The Michigan whetstone around the Jackson Iron Mine received much higher mention and was purported to be one of the best. So in finding out you like the Hindostan, my excitement increases should I ever get my hands on one of the Michigan stones that are incidentally among some of the oldest rock on the planet earth.

Chris L