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If salt is made of ions in a giant lattice, surely if I have two crystals they would attract each other and fuse? Or maybe the ions can't get close enough to each other to attract, or the surface is made of a different, neutral material?

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Sodium chloride ("salt") is made of a giant lattice of ions: Na+ and Cl-.

The crystals overall do not have any net charge as the the number of chloride ions is equal to the number of sodium ions. So, overall, there will be no electrostatic force between crystals as they are neutral in the bulk compound.

On the surface, crudely and without getting into the detail of the crystal structure, the ions will alternate on the surface at an atomic scale. You might imagine that this creates atom-sized patches where there will be net positive or negative charges. Would these attract another crystal? Would these attract the patches of charge in another crystal if they were adjacent. Maybe, but only if the surfaces were both atomically flat and lined up exactly. In reality the surfaces are rough and there is no net charge so large salt crystals won't stick because of this effect.

So the intuition that some crystal made of ions should have strong electrostatic attraction to another similar crystal is wrong because of electroneutrality and the detail of the physical surface.

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