Lineations are linear geological features within rocks, representing a preferred orientation or alignment of elements. They are categorized based on their scale and distribution.

Penetrative Lineations: These occur pervasively throughout the rock body, visible at all scales.

• Types:

  1. Mineral lineation: Aligned elongate mineral grains (e.g., hornblende) within metamorphic rocks. (Diagram: Arrows showing preferred alignment of elongated mineral crystals).

  2. Stretching lineation: Elongated clasts, pebbles, or fossils, indicative of maximum extension. (Diagram: Deformed, stretched ovoid shapes aligned in a common direction).

  3. Crenulation lineation: Micro-fold hinges on foliation surfaces. (Diagram: Wavy lines showing micro-folds with parallel hinges on a larger planar surface).

• Genesis: Reflect intense ductile deformation involving bulk strain and material flow, causing reorientation and elongation of components.

Non-penetrative Lineations: These are localized and do not occur uniformly throughout the rock mass.

• Types:

  1. Intersection lineation: Formed by the intersection of two planar features (e.g., bedding and cleavage). (Diagram: Two intersecting planes creating a visible line on their common surface).

  2. Boudinage: Elongated, segmented lenses of a competent layer within a less competent matrix, due to extension. (Diagram: A layer broken into sausage-like segments).

• Genesis: Formed by geometric intersection of features or localized brittle/ductile extension within specific layers.