Abstract
(010)[001] dislocations in K-feldspars have been studied by transmission electron microscopy using weak-beam and high-resolution techniques. It appears that (010)[001] dislocations are dissociated according to the reaction: [001]→[001]/2+[001]/2. The planar defect separating the partial dislocations is parallel to (010), the displacement vector being R = [001]/2. The energy estimated from the defect width (about 10 nm) is γ = 0·06 J m−2. Structural models of (010) planar defects were investigated. The planar defect most consistent with the observations lies within the double crankshaft chains of tetrahedra T-O4 (T = Si or Al) of the feldspar structure. This result leads to earlier ideas on dislocation glide being reconsidered.