Hi all,
We have a 20 yard pile of rotten Granite we use to patch the drive way when it needs it. I just use a 1/4" hardware cloth to screen a couple of scoops and save what comes through for the chickens. They have it free choice from young on. If I want more fine stuff, just pass it through a 1/8" screen or better yet let the chickens pick the sizes they want.
Sure Granite is best, but other rock will work. Find a gravel pit or a place that sells road gravel, grab your screens you can make enough grit to last a very long time for pennies. Heck you could even use the course material in builders sand. (Not the fine smooth tumbled play or beach sand.)
Honestly,
Why spend money on exotic rocks shipped from across the country? Find something local. Rock is cheaper than dirt!!!! Chickens have been domesticated for many thousands of years! I am pretty confident those chickens used indigenous rock as grit.
(I have a PVC pipe feeder I learned how to make here on BYC, which is filled with grit, so they can have it free choice in the coop in winter.)
on