Bill Tindall
If I read correctly one of these stones is not silicon carbide? I have been curious what the composition of the various synthetic stones were, supposing all were some variety of aluminum oxide with the more modern ones one of the newer forms of aluminum oxide (seeded gel/ceramic, etc).

If you know the mineral composition of these various stones I would find it of interest to reveal this information, ideally in a new post.

Why? Well, the composition will tell one a lot about what the stone can do. Silicon carbide will cut the hardest alloying carbides in the more abrasion resistant steels where as aluminum oxide is much less effective. However, unless some materials advance has been made silicon carbide is brittle and it easily crushes to finer particles when used in coarser grits. A ceramic or seeded gel aluminum oxide particle will maintain fresh cutting edges without having to shed particles to do so. Hence, a harder stone can be made that will be more resistant to wearing unflat. Etc. .......

The sharpening stone market must be tiny and I would presume it will not support materials research.?. Any insight on where developments in materials for sharpening is coming from (some larger market)? Are there any stones employing one of the boron abrasives?