What resource gathering books have you read besides "Mining for High Quality Granite", if any?
There is a base 10% chance to find high quality granite. Previously, while mining for granite you were almost always (since you are at least GM mining) guaranteed to dig up metal if you failed to find granite, using up the metal in the resource chunk relatively quickly. Now that you can't mine up metal with the new tool setting you are guaranteed to pull only granite out of the resource chunk, resulting in much higher overall granite yields from a single resource chunk. The success rates have not changed.
There are 2 books
Mining for Quality Stone
And
Making Valuables with Stonecrafting
I ate them both ( You need to be a GM Carpenter to use the second one)
While your tool is set to mining ore, you get ore every time (if you're GM Mining) until there is no metal left to mine.
While your tool is set to mine stone, you get a lot of *Error (MegaCliloc) : StringId Not Found* Which I assume is
You fail to find any stone
In theory, since every time you mine set to ore, you get ore, then every time you mine set to stone ,you should get stone, until the area is mined out.
That 10% chance to get granite while mining for ore AND granite makes sense...but if you're just mining for stone, you should get at least one every time.
I just went through a 50 use pickaxe and got 4 stones....