Sebastian (Doorsch) bought a small stone from UK a couple hours ago that I'm 80-90% sure is another of these, so hopefully he'll be able to comment on it when it arrives.
Got that stone you mentioned today....iam not shure if this is comparable ...iam shure its not a Coticule and in a certain way its comoarable to the other greenish stone i own...
The stone looks to me like a light green/olive tone with kind of lightbrown/beige swirls...or the other way around....
I created a slurry with a DMT it took me around 30sec. Until the slurry was created.
Several laps (30) with a Kitchen knife and slurry seems to work quite fast...