Re: To sift or not to sift; small stones okay?
I do believe, I could be wrong, granite is a common component of glacial rock dust used as a soil amendment. My understanding is that soil microorganisms will 'skuff' , as AaronTT described it, minerals from the stone's surface which eventually gets to the associated plants. If it were me, I probably wouldn't bother re-sifting unless there is an inordinate amount of stone in the mix. I do all my sifting with 1/2" hardware cloth and have never felt the need to go finer.
Who keeps calling me nuts??