"Overburden rocks have undergone high temperature pyrometamorphism during the Hanna II UCG experiment. Paralava rock, buchites and paralava breccias have formed due to various degrees of melting. New high temperature minerals such as oligioclase, clinopyroxene, ferrocordierite, anorthoclase, and tridymite have formed and the textures indicate that some of these crystallized directly from the melt. Rounded blebs of elemental iron have also been found in the paralava. The mineralogy and melting relations of the paralava, aso fusion temperatures determined on samples from the Hanna II coal, and thermocouple measurements made during the experiment all indicate that temperatures in excess of about 19800p (10820 C) were attained, and temperatures as high as 23500 p (1290oC) may have been reached. The color of the rocks, the presence of a reduced iron bearing silicate mineral (johannsenite) and blebs of native iron indicate that the experimental burn was reducing in the area of paralava formation. The product gas species were also reducing. Data from this study will prove useful in assessing the changes in groundwater chemistry that may result from underground coal gasification projects."