If the crack is tight - that is there is no fissure, you should use a penetrating epoxy to fill it and strengthen it.
http://www.defusco.com/stoneweld-crack-filler-epoxy-24oz-p-1982.htmlThis stuff is like water & will penetrate through the crack so the crack will not get larger.
After that has cured and you are not worried about the structural integrity of your countertop you should fill the crack ( if necessary) with our crack repair kit.
http://www.defusco.com/granite-marble-chip-repair-kit-p-2476.htmlIn the future when you are moving a slab, try rodding it first for reinforcement. Just cut a slot in the bottom of the slab and glue in a piece of steel (metal fishtape or 1/4" x 1/8" metal stock.
Mark