page_title: Joint (geology)
section_title: Fractography
hierarchical_section_title: Joint (geology) / Fractography
caption_attribution_description: English: Plumose fracture patterns in North Canyon, Arizona
context_page_description: A joint is a break of natural origin in the continuity of either a layer or body of rock that lacks any visible or measurable movement parallel to the surface of the fracture. Although they can occur singly, they most frequently occur as joint sets and systems. A joint set is a family of parallel, evenly spaced joints that can be identified through mapping and analysis of the orientations, spacing, and physical properties. A joint system consists of two or more intersecting joint sets.
  The distinction between joints and faults hinges on the terms visible or measurable, a difference that depends on the scale of observation. Faults differ from joints in that they exhibit visible or measurable lateral movement between the opposite surfaces of the fracture. As a result, a joint may have been created by either strict movement of a rock layer or body perpendicular to the fracture or by varying degrees of lateral displacement parallel to the surface of the fracture that remains “invisible” at the scale of observation.
  Joints are among the most universal geologic structures as they are found in most every exposure of rock.
context_section_description: Joint propagation can be studied using the techniques of fractography in which characteristic marks such as hackles and plumose structures can be used to determine propagation directions and, in some cases, the principal stress orientations.
caption: Plumose structure on a fracture surface in sandstone, Arizona
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