Characterisation of Raw Materials for Glass Manufacturing in the Past in the West Slovenia

Saso Sturm (saso.sturm@ijs.si)¹ & Breda Mirtic²

¹ Jozef Stefan Institute, Jamova 39, SI-1001 Ljubljana, Slovenia

² Faculty of Sci. and Eng., Dept. of Geol., As(breve)kerceva 12, 1000 Ljubljana, Slovenia

It is quite hard to determine the raw materials for manufacturing of the archaeological glass. Results of detailed chemical investigations of glasses fragments and possible raw materials are compared to prove the correlation. Chemical analysis of the glass fragments and possible raw materials from the Trebus(breve)a valley (Slovenia) was made. Glass samples were graded according to the colour intensity. Results of the chemical analysis proved that manufacturers used only a limited number of raw materials containing high amounts of silica. A deficient technology was used in the Trebus(breve)a glass-making workshop in the beginning of the 18^th century. Anyway, glasses of two types were recognized among the glass fragments found in the Trebus(breve)a valley. Glass with the higher amount of silica and low amount of impurities was characterised as the colourless glass. Coloured glass samples with relatively low amount of silica and quite high amount of impurities are the other type of glass. Glasses with higher amounts of the Al₂O₃ and Fe₂O₃ are often green and brown coloured. Geological investigation of the territory of the Trebus(breve)a valley gave two possible sources of the silica; the quartz enriched sandstone and flint. Both are of the Carnium age. The amount of silica is higher in the flint while the amount of impurities is higher in sandstone. The amounts of the silica and alumina in the flint are in agreement with their amounts in the colourless glasses. Contemporary are their amounts distinctively different in the sandstone and in the coloured glasses. The same relationship was proved for the amounts of the TiO₂ and Fe₂O₃.

The Solubility of H₂O and CO₂ in Rhyolitic Melts in Equilibrium with a Mixed CO₂-H₂O Fluid Phase

Nathalie Tamic (n.tamic@mineralogie.uni-hannover.de), Harald Behrens & François Holtz

Inst. für Mineralogie, Uni Hannover, Welfengarten 1, 30167 Hannover, Germany

H₂O and CO₂ solubilities in a natural rhyolite melt (Erevan Dry Fountain, Armenia) in equilibrium with H₂O-CO₂ fluids were determined at 200 and 500 MPa and at 800 and 1100°C. The composition of the fluid phase after experiment was mostly determined by gravimetry. Water and CO₂ contents of the glasses were measured using IR spectroscopy. At 200 MPa, the water solubility turn over from a square root dependence on mole fraction of H₂O in the fluid phase (X^f_H2O) at low X^f_H2O to a linear dependence above X^f_H2O=0.25. At 500 MPa a similar trend is observed up to about 5 wt% dissolved water. At higher X^f_H2O, however, the dependence of water solubility on X^f_H2O is more pronounced. A negative T-dependence of water solubility is observed in the whole experimental range at 200 MPa. At 500 MPa the T-dependence of water solubility changes from positive at high X^f_H2O to negative below X^f_H2O=0.75. An empirical model to predict water solubility in rhyolitic melts in the P-T range 75-500 MPa and 800-1100°C was derived from our new solubility data and data from Blank et al. (1993). The model reproduces our data within ±5% relative.

The CO₂ solubility shows a non-linear dependence on X^f_CO2 with deviation from linearity increasing with pressure. The maximum CO₂ solubilities (equilibrium with pure CO₂) predicted from the data trends are 0.28 ±0.03 and 0.11 ±0.01 wt% at 1100°C and 200 and 500 MPa, respectively. At 800°C, the solubility of pure CO₂ cannot be determined because of melt crystallisation. The T-dependence of CO₂ solubility is found to be almost negligible at 200 MPa and slightly positive at 500 MPa. Our experimental solubility data at 200 MPa are slightly better reproduced by the model of Papale (1999) than with that of Holloway and Blank (1994).

Blank JG, Stolper EM & Carroll MR, Earth Planet. Sci. Lett, 119, 27-36, (1993).

Holloway JR & Blank JG, Rev. Mineral.:Volatiles in magmas. Mineral. Soc. Am, 30, 187-230, (1994).

Papale P, Am. Mineral, 84, 477-492, (1999).