True Herkimer Diamond crystals are stubby and double terminated and tend to grow in branching clusters, which means that their surface may exhibit indentations, keys or natural damage where they have separated from their clusters or from groundmass during the extraction process. This natural damage does not affect their energies. The extraction process also may result in splitting or fracturing of the crystals - once again this does not affect their energies, but will mean that they might not be able to be used as you might a fully double terminated specimen.
From a metaphysical point of view Herkimers are one of the best holders and carriers of full spectrum Light and can powerfully recharge a depleted energy system AND are very efficient cleansers of negativity. They will also provide clarity in all thinking and reasoning processes.