Dislocations in calcium fluoride

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Abstract
The cleavage faces of transparent calcium fluoride crystals collected from Amba Dungar of Chhota-Udepur, Gujarat State, have been etched and the etch pattern has been optically studied. It is observed that the point-bottomed pits are eccentric. By etching matched pairs of cleavage faces for successively different periods, it has been shown that point bottoms of the point-bottomed pits follow linear path. It is also observed that the eccentricity in the case of matched pits on matched faces is in the same sense. The eccentricities of the pits have been explained by postulating the existence of inclined linear dislocation lines in the body of the crystal. The inclinations of the dislocation lines have been computed from the measurements made on the pits, and it is observed that they are the same in case of matched pits on matched pairs. Thus it is conjectured that the pits nucleate at the site of inclined dislocation lines. This is also confirmed by etching the matched faces, one by one etchant and the other with a different etchant. It is shown that dislocation lines have different inclinations, but large majority of them are inclined at angles between 16° to 20° with the normal to the cleavage face.
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