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Fracture of Gems




Fracture is the way a mineral breaks other than along cleavage planes and is described in terms of the shapes resulting from the fracture of the material. The most distinctive type of fracture is conchoidal (shell like) which results in concentric concave ridges. This is the common type of fracture in glass type materials such as Obsidian. Quartz, Opal and Peridot also break with conchoidal fracture (in other than cleavage directions).

Types of fracture are:

  • Conchoidal (shell like) which results in concentric concave ridges
  • Subconchoidal, which is similar to conchoidal but less prominant, often lacking the concentric ridges.
  • Even. A fairly smooth, flat break that may visually resemble a cleavage plane.
  • Granular. A fine-grained break resembling the surface of a sugar cube.
  • Spintery. A fibrous break that resemles splintered wood.
  • Uneven. A general catagory used to describe fractures with an irregualr appearance such as aggregate gem materials like Serpentine.
  • Steplike. Breaks that may be a combination of cleavages in more than one direction or a combination of cleavages and fractures.

Fracture, along with cleavage, can be of important diagnostic value in determining a type of unknown mineral.


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