Dives for cover for fear of flying rocks!

Sorry about that!

The other stone does indeed look like a Noviculite as well. There are no hard and fast rules for what one should look like, And they come in coarseness grades as well! There are loads of colour variations some look layered and banded. Others have spots or are all one nice colour! Some are translucent, other totally black or grey.

They work out the grade by measuring the density of the stone. The most dense stones are the finishing grades. The least dense have more airspace and pores and cut more aggressively and faster.

You can google specific gravity equations if you are wanting to go that route. Then compare it to the gravity formula used by Dans whetstone.

https://en.wikipedia.org/wiki/Specific_gravity

https://www.danswhetstone.com/inform...ne-grades-101/