Pic of the day #36 (Rock fabric)

Pic src: Earth structure – An introduction to structural geology and tectonics

Left figure: The basic categories of fabrics. (a) A random fabric. The fabric elements are dark, elongate crystals. The long axes of these crystals are not parallel to one another. (b) A (1-dimensional) preferred fabric, in which the long axes of elongate crystals are aligned with one another. (c) A foliation. The fabric elements are planar and essentially parallel to one another, creating a 2-dimensional fabric. (d) A lineation. The fabric elements are linear; in this example, we show the alignment of fabric elements in a single plane.
Right figure: The distinction between continuous and spaced fabrics. (a) A continuous fabric. The lines represent a planar fabric element that continues to be visible no matter how small your field of view (at least down to the scale of individual grains). (b) A spaced fabric. The rock between the fabric elements does not contain the fabric. The circled areas represent enlarged views.


    1. Foliation and Lineation fabric of rock are formed under directional stress, i.e. the differential stress. Tectonites are deformed metamorphic rocks with preferred orientation of grains depending on the stress direction of differential stress.
      You will find such rocks with in the thrust sheet all along the Himalayas!
      Flinn diagram is a mathematical way to understand whether the rock will show L, LS, SL or S fabric depending upon the ratio of principle axis (X>Y>Z) in the deformed grains.
      Prolate for L and Oblate ellipsoid for S fabric.

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