what size particles are they now?
the bag i bought is unbelievably fine to begin with
i use it in pots for annuals and it seems to make a difference
i think it should be ok as is
a little goes a long way.. i give each plant a half a teaspoon
It comes in two forms, powdered, and pellet form. I live in Utah (where it's mined), and I've only ever seen the pellet version for sale here. I'd prefer the powdered, but I would guess the pellet form wouldn't take too much longer to break down compared to the powdered.
I'd guess your grinder would be ruined in a short amount of time. Maybe a hammer and a couple of ziplock bags might be better if it's just a small amount you wanted to crush.
I throw it in my compost pile and feed some to my chickens. I don't put it directly on my garden beds anymore. By the time the compost goes to the garden, I figure it's been broken down to a usable point.
Have fun (wear glasses, if you try crushing it).
Social distancing since 1975.
Diego Footer on Permaculture Based Homesteads - from the Eat Your Dirt Summit