Thermodynamic mixing properties of Rb-K feldspars

Hydrofluoric acid solution calorimetric measurements conducted at 50 °C on a series of Al-Si ordered Rb-K feldspars reveal that the enthalpies Rb-K mixing (Hex) for this series are positive, with maximum values skewed toward Rb-rich compositions. However, the magnitudes of Hex are greatly reduced relative to those for Na-K feldspars, as are the positive volumes of Rb-K mixing observed for this series. Both observations can be explained by the substitution of two ions that are relatively similar in size. The difficulty in synthesizing Rb-rich sanidine via Rb-exchange of K-sanidine, contrasted
with the ability to synthesize rubicline from K-microcline by such exchange, together with a vanishingly small ΔV between ordered rubicline and disordered Rb-sanidine suggest that the volume of Rb-feldspar is close to the limit to which the feldspar structure can be expanded at 1 bar.

Title	Thermodynamic mixing properties of Rb-K feldspars
Creator	Roux, J.
Creator	Hovis, Guy L.
Publisher	American Mineralogist
Academic Department	Geology & Environmental Geosciences
Division	Natural Sciences
Organization	Lafayette College
Date Issued	2008
Date Available	2010-01-08T16:15:36Z
Type	Article
Language	English
Keyword	Rb-K feldspars
	mixing properties
	thermodynamics
	solution calorimetric data
Bibliographic Citation	Hovis, G. L., J. Roux. (2008). "Thermodynamic mixing properties of Rb-K feldspars." American Mineralogist 93: 1597-1602.
Standard Identifier	DOI 10.2138/am.2008.2791
Standard Identifier	Handle 10385/545
Permalink	http://hdl.handle.net/10385/545
Rights Statement	In Copyright
Rights Holders	Mineralogical Society of America