Sentence:  Notice that <WSD>cleavage</WSD> has nothing to do with imperfections in the crystal. Indeed, if you try cleaving an imperfect crystal, you may find that it cannot be cleaved as well as a perfect one. The <WSD>cleavage</WSD> is the result of the orderliness of the atomic arrangement. No wonder imperfections, which disturb the orderliness, disturb the <WSD>cleavage</WSD> as well. You will also note that the <WSD>cleavage</WSD> directions are obedient to the symmetry of the crystal. 
Meaning of the word marked with <WSD> tags:  The tendency of a crystal to split along specific planes. (from 19th c.)