It is shown that etch pits on a crystal may originate from the following two causes. One is a microscopic pit or an easily soluble minute portion or inclusion which exists accidentally and locally on the crystal surface, and the other is a dislocation existing in the crystal. In an etch pit of the first kind its depth is unchanged but its calibre increases as the dissolution or etching proceeds (the temporary etch pit), while both the depth and the calibre of an etch pit of the second kind increase in proportion to the etching time (the permanent or proper etch pit). A brief consideration is also made of the multiplicated etch pit as a variation of the permanent etch pit. Experimental evidences for the conclusions are presented.
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