Crushed granite is a very acceptable, inexpensive and readily available soil additive, despite what the Californians and California wanna-bees



say. Pumice is vastly expensive and mostly hard to come by on the East coast--despite what you hear.
However, more directly to answer the question asked,--if you're searching for specialized granite and are willing to pay for such a thing, you might as well use pumice. You're probably going to be about as lucky finding special granite and you're probably going to pay a premium for it. There are no extremely special qualities that granite has that can't be filled by pumice or a number of other ingredients. If you don't like the color, I'd search for haydite...expanded shale
I went out to the rockery today to shoot some pictures of supplies readily available in my area. I live in a modest town, not that big and surly close to the same size as Macon Georgia.
This California wanna-be has tried everything under the sun to grow plants in. I have used granite products, mostly DG in my soils. There is nothing wrong with using this as a soil additive if shear weight is what your after. Other than weight there is no other benifit from this component that could not be fullfilled with the simple addition of sand which is readily available everywhere.
A quick google search in
Macon Georgia turned up many possible places that will sell crushed rock products with this place even showing crushed brick, which I have used and find a very valuable soil component. It is not readily available to me or I would use it more.
My rock yard carries in bulk and pre bagged:
1/4 red and black lava. They were out of the black when I was there.
1/4 Cali-gold crushed rock. Pretty good stuff if adding rock to your soil is what your after.
1/4 DG (decomposed granite) grey in color and good size. Good if wanting rock again.
Sand, best component if no other good components available. Sand and potting soil 50/50 makes great bonsai soil.
1/4 brown crushed rock. I have no idea what this is, probably a crushed shale product, again good if you wish to add rock.
All my other components are imported Japanese soil products that I buy at bonsai conventions or bonsai dealers. They ain't cheap but they are best, cause they are bonsai soil specific and that means something. Will they make better bonsai? Probably not. I can afford them so I use them, your mileage may differ.
Cheers, Al