Crystallography
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Crystal twinning - Wikipedia, the free encyclopedia
... separates the two crystals. Crystallographers classify twinned crystals by a number of twin laws. ... These twin laws are specific to the crystal system. ...
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NIH MBI Laboratory for Structural Genomics and Proteomics
Perfect Merohedral Twinning involves a crystal with a twin fraction equal to or ... Output Format (Perfect Twinning Test Only) ...
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Twinning, Polymorphism, Polytypism, Pseudomorphism
Growth Twins - When accidents occur during crystal growth and a new crystal is added to the face of an already existing crystal, twinning can ...
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NIH MBI Laboratory for Structural Genomics and Proteomics
Twinning is a crystal growth disorder in which the specimen ... (T. O. Yeates (1997), Detecting and Overcoming Crystal Twinning. ... crystal twinning ...
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Mineral Gallery - THE TWINNED MINERALS
Twins are recognized by penetration angles or notches in the crystal, mirror ... Eventually a crystal composed of stacked twin layers is the result. ...
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Genesis of Twin Crystals
THE GENESIS OF TWIN CRYSTALS ... twin boundary region is a locus of higher ... To understand how twins develop during the growth of the crystal, one must be ...
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Twinning - Wikipedia, the free encyclopedia
City and town twinning; ... Crystal twinning in crystallography refers to intergrown crystal forms which ... "Twinning" is a jargon term in motion pictures for ...
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General Features of Twinning
The crystal of point group 2 can therefore form merohedrical twins with the ... The twin element belongs to the Laue class of the crystal, but not to the point ...
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Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals. Crystallographers classify twinned crystals by a number of twin laws. These twin laws are specific to the crystal system. The type of twinning can be a diagnostic tool in mineral identification.

Simple twinned crystals may be contact twins or penetration twins. Contact twins share a single composition surface often appearing as mirror images across the boundary. Plagioclase, Quartz, gypsum, and spinel often exhibit contact twinning. In penetration twins the individual crystals have the appearance of passing through each other in a symmetrical manner. Orthoclase, staurolite, pyrite, and fluorite often show penetration twinning.

If several twin crystal parts are aligned by the same twin law they are referred to as multiple or repeated twins. If these multiple twins are aligned in parallel they are called polysynthetic twins. When the multiple twins are not parallel they are cyclic twins. Albite, calcite, and pyrite often show polysynthetic twinning. Closely spaced polysynthetic twinning is often observed as striations or fine parallel lines on the crystal face. Rutile, aragonite, cerussite, and chrysoberyl often exhibit cyclic twinning, typically in a radiating pattern.

There are three modes of formation of twinned crystals. Growth twins are the result of an interruption or change in the lattice during formation or growth due to a possible deformation from a larger substituting ion. Annealing or Transformation twins are the result of a change in crystal system during cooling as one form becomes unstable and the crystal structure must re-organize or transform into another more stable form. Deformation or gliding twins are the result of stress on the crystal after the crystal has formed. Deformation twinning is a common result of regional metamorphism.

Of the three common crystal structures: body-centered cubic, face-centered cubic, and hexagonal close packed, the HCP structure is the most likely to twin.

Crystals that grow adjacent to each other may be aligned to resemble twinning. This parallel growth simply reduces system energy and is not twinning.

Twin boundaries surface with macroscopic crystalline features. Twin boundaries are visible as striations within each crystallite, most prominently in the bottom-left and top-right.

Twin boundaries occur when two crystals of the same type intergrow, so that only a slight misorientation exists between them. It is a highly symmetrical interface, often with one crystal the mirror image of the other; also, atoms are shared by the two crystals at regular intervals. This is also a much lower-energy interface than the crystallite that form when crystals of arbitrary orientation grow together.

Twin boundaries are partly responsible for shock hardening and for many of the changes that occur in cold work of metals with limited dislocation or at very low temperatures. They also occur due to martensite: the motion of twin boundaries is responsible for the pseudoelastic and shape-memory behavior of nitinol, and their presence is partly responsible for the hardness due to quenching of steel.

References

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7

External links

• Tulane Edu. crystal twinning
• Mineral galleries - twins
• Mathematical and Theoretical Crystallography
• Online Dictionary of Crystallography

Crystal twinning - Wikipedia, the free encyclopedia
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a ...

NIH MBI Laboratory for Structural Genomics and Proteomics
Perfect Merohedral Twinning involves a crystal with a twin fraction equal to or near 1/2. This test will attempt to determine the presence of twinning by comparing the diffraction ...

CCP14 Homepage - Single Crystal and Powder Diffraction - Methods ...
CCP14 Methods, Problems and Solutions Single Crystal Twinning Software and Web Resources The CCP14 Homepage is at http://www.ccp14.ac.uk

Twinning, Polymorphism, Polytypism, Pseudomorphism
Twinning in Crystals. Sometimes during the growth of a crystal, or if the crystal is subjected to stress or temperature/pressure conditions different from those under ...

Definition: twinning from Online Medical Dictionary
... also, rarely, in artificial twinning (accomplished for example by pressure), the process by which this reversal is brought about. Polysynthetic twinning, repeated twinning of crystal ...

crystal twinning - Wiktionary
Definition from Wiktionary, a free dictionary

High throughput techniques as a strategy to overcome crystal twinning
102 High throughput techniques as a strategy to overcome crystal twinning Stephen Carr, Simon Phillips and Chris Thomas Background Staphylococcal plasmids of the pT181 family use a ...

Research - Twinning
Information about the group and its activities. ... Twinning Twinning is not an uncommon effect in crystallography, although it has long been considered to be one of the most ...

Detecting and overcoming crystal twinning. [Methods Enzymol. 1997 ...
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Twinning - Wikipedia, the free encyclopedia
... of another one next to it, with a median in between (Canadian English), upgrading the road into a (usually) four-lane dual carriageway (divided highway); Crystal twinning in ...