Abstract: Two specimens of tremolite and one of richterite, all with nephrite jade texture, have been examined by transmission electron microscopy using ion-thinning for specimen preparation. The specimens contain clusters of very small lath-like crystallites with z-axes approximately parallel but in a range of azimuthal orientations. It is suggested that these clusters which are themselves in varied orientations are the result of post-tectonic recrystallization of strained amphibole crystals, the new crystals inheriting the z-axis orientations of the old. The extreme toughness of nephrite jade is attributed to a number of the sub-microscopic features observed, including the sizes, habits, and orientations of its crystallites, and the nature of its grain boundaries.