Cleavage (crystal)


Cleavage (crystal)
Green fluorite with prominent cleavage.

Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye.[1]

Contents

Types of cleavage

Cleavage forms parallel to crystallographic planes:[1]

Biotite with basal cleavage.
  • Basal or pinacoidal cleavage occurs parallel to the base of a crystal. This orientation is given by the {001} plane in the crystal lattice (see Miller indices), and is the same as the {0001} plane in Bravais-Miller indices, which are often used for rhombohedral and hexagonal crystals. Basal cleavage is exhibited by the mica group and by graphite.
  • Cubic cleavage occurs on the {001} planes, parallel to the faces of a cube for a crystal with cubic symmetry. This is the source of the cubic shape seen in crystals of ground table salt, the mineral halite. The mineral galena also typically exhibits perfect cubic cleavage.
  • Octahedral cleavage occurs on the {111} crystal planes, forming octahedra shapes for a crystal with cubic symmetry. Diamond and fluorite exhibit perfect octahedral cleavage. Octahedral cleavage is seen in common semiconductors. For lower-symmetry crystals, there will be a smaller number of {111} planes.
  • Dodecahedral cleavage occurs on the {110} crystal planes forming dodecahedra for a crystal with cubic symmetry. For lower-symmetry crystals, there will be a smaller number of {110} planes.
  • Rhombohedral cleavage occur parallel to the {1011} faces of a rhombohedron. Calcite and other carbonate minerals exhibit perfect rhombohedral cleavage.

Parting

Crystal parting occurs when minerals break along planes of structural weakness due to external stress or along twin composition planes. Parting breaks are very similar in appearance to cleavage, but only occur due to stress. Examples include magnetite which shows octahedral parting, the rhombohedral parting of corundum and basal parting in pyroxenes.[1]

Uses

Cleavage is a traditional physical property used in mineral identification both in hand specimen and microscopic examination of rock and mineral studies. As an example, the angles between the prismatic cleavage planes for the pyroxenes (88–92°) and the amphiboles (56–124°) are diagnostic.[1]

Crystal cleavage is of technical importance in the electronics industry and in the cutting of gemstones.

Precious stones are generally cleaved by impact as in diamond cutting.

Synthetic single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave. Simply pressing a silicon wafer against a soft surface and scratching its edge with a diamond scribe is usually enough to cause cleavage; however, when dicing a wafer to form chips, a procedure of scoring and breaking is often followed for greater control. Elemental semiconductors (Si, Ge, and diamond) are diamond cubic, a space group for which octahedral cleavage is observed. This means that some orientations of wafer allow near-perfect rectangles to be cleaved. Most other commercial semiconductors (GaAs, InSb, etc.) can be made in the related zinc blende structure, with similar cleavage planes.

See also

References

  1. ^ a b c d * Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, ISBN 0-471-80580-7

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • cleavage crystal — noun : a crystal fragment having a regular form because bounded by cleavage faces …   Useful english dictionary

  • Cleavage — may refer to: Cleavage (breasts), partial exposure of the separation between a woman s breasts. Cleavage enhancement, methods of making a person s breast cleavage look more substantial than it really is. Buttock cleavage, minor exposure of the… …   Wikipedia

  • Cleavage (geology) — This article is about rock cleavage, for cleavage in minerals see Cleavage (crystal) Different ways in which a cleavage can develop in a sedimentary rock. A: original sedimentary rock; B: pencil cleavage; C: diagenetic foliation (parallel to… …   Wikipedia

  • Crystal structure — In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice… …   Wikipedia

  • Crystal system — Diamond crystal structure consists of face centered cubic lattice. In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals.… …   Wikipedia

  • Crystal habit — This article is about the descriptive term used in mineralogy. For the addictive drug, see crystal methamphetamine. Pyrite sun (or dollar) in laminated shale matrix. Between tightly spaced layers of shale, the aggregate was forced to grow in a… …   Wikipedia

  • Cleavage — Cleav age, n. 1. The act of cleaving or splitting. [1913 Webster] 2. (Crystallog.) The quality possessed by many crystallized substances of splitting readily in one or more definite directions, in which the cohesive attraction is a minimum,… …   The Collaborative International Dictionary of English

  • Cleavage and polyadenylation specificity factor — (CPSF) (or Cleavage polyadenylation stimulating factor) is involved in the cleavage of the 3 signaling region from a newly synthesized pre messenger RNA (pre mRNA) molecule in the process of gene transcription. It is the first protein to bind to… …   Wikipedia

  • Crystal Storm — is an entertainer and model.Early yearsCrystal Storm was born November 14th. Her height is convert|5|ft|2|in|m|2 and her weight is convert|135|lb|kg. She grew up in Southern California.CareerCrystal Storm s fan club/mailing address is: Crystal… …   Wikipedia

  • Crystal chemistry — is the study of the principles of chemistry behind crystals and their use in describing structure property relations in solids. The principles that govern the assembly of crystal and glass structures are described, models of many of the… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.