X-ray study of deformation lamellae in olivines of ultramafic rocks

Summary. Olivine crystals howing (100} deformation lamellae between crossed po]ars how spots streaked out transversely to 00l layer lines in X-ray oscillation photographs. Compositional inhomogcneity is ruled out by optics and electron microprobe analysis. Structurally controlled gliding on {100} (plane of greatest atom density) in the direction [001] (close-packing direction) is deduced on analogy with deformed metals. Mechanism of lamella formation is discussed in terms of superincumbent load; but it is concluded that pressures due to crystal growth are mainly responsible. U NDULOSE extinction and deformation lamellae (sometimes called translation lameUae) in oSvines from ultramafic rocks and nodules have been described by numerous authors including the well-known studies by Turner (1942) and Chudoba and Frechen (1950). More re-cently Raleigh (1965) and Riecker and Rooney (1966) have studied the glide systems in experimentally deformed olivines. Although these authors have studied the deformed olivines by various optical methods