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Science 18 September 1992:
Vol. 257. no. 5077, pp. 1669 - 1672
DOI: 10.1126/science.257.5077.1669
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Articles

Exsolution of Hornblende and the Solubility Limits of Calicum in Orthoamphibole

Eugene A. Smelik 1 and David R. Veblen 2

1 Department of Geological and Geophysical Sciences, Guyot Hall, Princeton University, Princeton, NJ 08544
2 Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218

Exsolution between orthorhombic and monoclinic amphibole has been postulated for many years on the basis of crystal-chemical and structural differences. Transmission and analytical electron microscope examination of calium-rich gedrite specimens from southwestern New Hampshire has now revealed evidence for exsolution of calcic clinoamphibole (hornblende) from ferromagnesian orthoamphibole. Analytical electron microscopy data suggests that calcium has a low solubility limit in the orthoamphibole structure. The hornblende lamellae range from only a few unit cells in thickness to about 80 nanometers. The formation of the calcic amphibole lamellae resulted from heterogeneous nucleation and growth along pre-existing (100) stacking faults. Thus, the deformation processes producing the stacking faults played a key role in preparing the sites for exsolution.

Submitted on May 21, 1992
Accepted on July 20, 1992


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Metamorphic Amphiboles: Composition and Coexistence.
J. C. Schumacher (2007)
Reviews in Mineralogy and Geochemistry 67, 359-416
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An occurrence of igneous orthorhombic amphibole, Eriksberg gabbro, southern Sweden.
D. T. Claeson and W. P. Meurer (2002)
American Mineralogist 87, 699-708
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High-Resolution and Analytical Transmission Electron Microscopy of Mineral Disorder and Reactions.
D. R. Veblen, J. F. Banfield, G. D. Guthrie Jr., P. J. Heaney, E. S. Ilton, K. J. T. Livi, and E. A. Smelik (1993)
Science 260, 1465-1472
   Abstract »    PDF »


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