| Abstract: | Coexistence of twisted and untwisted crystals is explained via a model that accounts for the coupling of the entropic and energetic effects of impurities and a supra-lattice-scale structural order parameter. It is shown that twisted impure crystals can be in equilibrium with untwisted purer ones. The model explains how coexistence can occur in agates and other systems under hydrostatic stress. The model implies that untwisted crystals grown under one set of conditions could undergo a phase separation that, when accompanied by an imposed compositional gradient, leads to commonly observed, alternating bands of twisted and untwisted crystals and, when occurring in the absence of an external gradient, mossy patterns of crystal texture can emerge. This phenomenon is not related to anisotropic applied stress. Rather coexistence is a consequence of a compositional segregation/twist phase transition. Since twist coexistence is a compositional equilibrium, it arises from the exchange between bulk phases; hence, the detailed nature of the atomic structure within an interface between twisted and untwisted zones is not relevant. The approach places crystal-twist phenomena within the theory of order/disorder phase transitions. |
| Genre: | Article |
| ProdID: | 70031454 |
| Citation Author: | Comer, J.; Ortoleva, P. |
| Citation Contributing Office: | |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | |
| Citation Editor: | |
| Citation End Page: | 1957 |
| Citation Issue: | 11-12 |
| Citation Keywords: | |
| Citation Language: | English |
| Citation Larger Work Title: | American Mineralogist |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | 6 |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | |
| Citation Projection: | |
| Citation Public Comments: | |
| Citation Publisher: | |
| Citation Series: | |
| Citation Series Code: | |
| Citation Series Number: | |
| Citation Search Results Text: | Coexistence of twisted and untwisted crystals: An impurity/structural order model with implications for agate patterns; 2007; Article; Journal; American Mineralogist; Comer, J.; Ortoleva, P. |
| Citation Start Page: | 1952 |
| Citation Volume: | 92 |
| Citation Year: | 2007 |
| Type: | citation/reference |
| Text: | Coexistence of twisted and untwisted crystals: An impurity/structural order model with implications for agate patterns; 2007; Article; Journal; American Mineralogist; Comer, J.; Ortoleva, P. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.2138/am.2007.2547 |
| Date Other: | Mon, 1 Jan 2007 00:00 -0600 |
| Publisher: | |
