The etching of crystal cleavages II. Diamond octahedral cleavages

Abstract

Abstract The etch patterns formed on octahedral cleavages of diamond are studied optically. It is established that etch pits are distributed in three ways (a) random small pits, (b) striking linear arrangements, (c) individual isolated pits usually larger than the others. By etching oppositely matched cleavages it is demonstrated that there is a remarkable degree of coinci­dence and matching (in mirror image) of the etch patterns. There is generally one-to-one correspondence between centres of isolated pits and of linear patterns. It is shown too that cleavage ledges displace sideways owing to an alternative solution process which takes place without creation of visible etch pits in certain regions. The observations can be accounted for by postulating that the cleavage cuts through crystal imperfections with each such imperfec­tion becoming the nucleus of a pit. Pit concentrations found vary from 103 to over 107/mm2 and some small regions are quite free from imperfections. By etching cleaved blocks a striking stratigraphy is revealed and it is proved that the indi­vidual stratigraphical sheets go right through the whole crystal. The etch strata therefore reveal for the first time the whole growth history of the diamond. The implications are briefly discussed. The etching reveals small ring cracks on the cleaved faces and these probably originate from the shock of cleavage.