Originally Posted by
Euclid440
Looks and sounds possibly like a Charney Forrest, greenish blue with brown and grey streaks. They are Novaculites similar to a hard Ark in performance, some will finish razors and are great knife stones, especially Carbon Steel knives.
They can be finished and burnished for a fine finisher. They were traditionally “Oil” stones but work just fine with water and a drop or two of Ballistol or Smiths Honing oil.
If it was caked in oil, it may take some soaking to get all the oil out. I soak in Simple Green or Awsome and water, it can take week or month to get it to release all the oil. Keep changing the water and degreaser until the water stops darkening.
Nice find, try finishing one side to 600 grit and burnishing the other.