Friedrich A. Seifert

Structural similarity of glasses and melts relevant to petrological processes

High-temperature Ramun spectroscopic investigations of melts in the systems GeO2. Na2O-SiO2 and Na2O-Al2O3-SiO2 demonstrate the close structural relationships between melts and glasses. No coordination changes with temperature and no new anionic species have been observed in the melt relative to those in the glass. The relative concentration of different anionic units changes only slightly in the temperature range 100–1350 C. With increasing temperature, compositions with three-dimensionally connected structural units exhibit an intensity increase of a band characteristic of a defect in the network structure, but the network still remains essentially intact.

Kinetics of the Fe2+-Mg, Order-Disorder Reaction in Anthophyllites: Quantitative Cooling Rates

The kinetics of the Fe2+-Mg, order-disorder phenomenon in a highly ordered natural anthophyllite have been determined over the temperature range from 400� to 720�C at a pressure of 2 kilobars. At temperatures of 600�C and above, equilibrium is attained by disordering as well as ordering reactions. The intracrystalline exchange is defined by a standard Gibbs free energy of 4247 � 54 calories per formula unit. Rate studies at 550� and 500�C show that equilibrium is attained by ordering but not by disordering within the same time scale and that the exchange reaction is characterized by an activation energy of∼55 kilocalories per formula unit. An equilibration temperature for the natural anthophyllite of 270�C is determined from the termination of the ordering process owing to excessively slow reaction kinetics after∼107 years. From the rate constants of the exchange process, for different crystallization temperatures, the apparent equilibration temperature of 270�C defines a maximum linear cooling rate for the rock of 1 x 104�C per year.