Studies of helical dislocations,polygonization and pile-ups of dislocations in magnesium orthosilicate single crystals

(010) cleavages of magnesium orthosilicate crystals have been etched in concentrated hydrochloric acid and in its vapour at room temperature and also in the melts of sodium and potassium hydroxides at 400 °. Evidences of helical dislocations with their axes along [100] and [001] directions as revealed by etching is reported. Observations of polygonizations and pile-ups of dislocations are described and the implications are discussed.