Pressure shadows. The dark, almost round, objects are rigid pyrites. During deformation they do not deform, but the deformation of the surrounding matrix pulls the latter away from the pyrite. The space between is filled with precipitate. Strain can be estimated by comparing the form of the precipitate/matrix boundary with the edge of the pyrite. Root zone of the Morcles nappe, Rhone valley, Switzerland. (photo: Martin Casey)
