Diffusion in coronas around clinopyroxene: modelling with local equilibrium and steady state, and a non-steady-state modification to account for zoned actinolite-hornblende

Article Abstract:

A reaction rim or corona forms between two minerals closely apposed. Retrograde coronas are the result of diffusion kinetics of the component minerals of the different layers of an actinolite-hornblende system. A model of the layer structure of the system is created and the diffusion coefficients of the different mineral components calculated. Results indicate that calcium diffuses more than aluminum. Silicon is relatively immovable because of saturation. On the other hand, magnesium diffuses towards the source. The implication of the model on the mineral structure of rocks is discussed.

Amphiboles, Hornblende

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The mechanisms of water diffusion in polymerized silicate melts

Article Abstract:

Water diffusivity in albitic and quartz-orthoclasic melts is identical with that of haplogranitic melts. Using the same P-T condition and water content, anhydrous composition of haplogranitic melts has been found to have little effect on water mobility in polymerized albitic and quartz-orthoclasic melts. However, the degree of polymerization wields a strong influence. Concentration-distance profiles measured by FTIR microspectroscopy determined the chemical diffusion coefficients of water.

Silicates

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An experimental investigation on diffusion of water in haplogranitic melts

Article Abstract:

An experiment on the diffusion of water in haplogranitic melts of anhydrous composition reveals that the water diffusivity rises with water content (less than)3 wt% but at higher water contents. Using the diffusion couple approach, the study shows a drop in activation energy from 64(+-)10kJ/mole for 0.5 wt% water to 46(+-)5kJ/mole for 4 wt% water. However, activation energy remains at a constant level at higher water content.

Granite

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