Should work just fine.
I regularly use quartzite as a grit component in my mixes (subbing it for granite), and I've never had an issue. If anything, the sharp edges are a bonus (inducing root-branching via abrasion).

Josh

Guess I can't comment long term
"cause I just recently started some over quartz crystals
But don't see any problems

Just removed the cup I had around this one a few days ago
So all the dirt & what not hasn't totally washed away yet

Awesome! Thank you for the info! I have a beautiful piece of black quartz crystals that I some day want to train a witch hazel over - I think the delicate yellow flowers will make a stunning contrast to the big black crystals. dethcheez - I would love to see a followup of your bonsai in the future if you think about it. Looks like it'll be really cool.

Here's a better pic
Now that I got it cleaned up