Dolomite has the wrong magnesium/calcium ratio. It could bind up your soil. Oyster shell flour and aragonite flour are pure forms of calcium carbonate...much better sources. Hi-cal agriculture lime also a nice choice. I personally use 1/2 cup aragonite flour and 1/2 cup of gypsum in my no til garden and don't see much problems. I also use crab shell, rock dust, kelp, and neem as hyroot mentions but not necessarily for their calcium content.