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H. J. GREENWOOD, The Synthesis and Stability of Anthophyllite, Journal of Petrology, Volume 4, Issue 3, 1963, Pages 317–351, https://doi.org/10.1093/petrology/4.3.317
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Abstract
The pure magnesium orthorhombic amphibole, anthophyllite, has been synthesized and its upper and lower stability limits have been established by reversible hydrothermal experiments. The synthetic mineral has refractive indices nx=1·587±0·001, ny=1·602±0·005, nz=1·613±0·001, and unit-cell dimensions of a0=18·61±0·02 Å, b0=18·01±0·06 Å, c0=5·24±0·01 Å. The mineral is stable over a narrow temperature range in the presence of the phase H2O. At a PH2O of 1,000 bars the upper stability limit is 745°±10° C and the lower stability limit is 667°±8° C.
Rate studies indicate that anthophyllite can nucleate at temperatures above its upper stability limit by disintegration of talc sheets into strips of double chains. The activation energy for this process is 150±30 kcal mol−1.
Application of the data to rocks of the Balmat area, New York, suggests that the equilibrium pressure of water during the metamorphism was significantly less than the total pressure. The data indicate that monomineralic zones of anthophyllite in ultramafic rocks are due to the presence of a steep gradient in the activity of H2O, or a steep gradient in temperature, or both, across the zones.
