Opening-mode fracture in siliceous mudstone at high homologous temperature--Effect of surface forces Peter EICHHUBL*, Atilla AYDIN, and Jason LORE Rock Fracture Project, Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305 * Also at Monterey Bay Aquarium Research Institute, Moss Landing, California 95039 Abstract. In analogy to high-temperature sintering of ceramics and metal powder compacts, the formation of opening-mode fractures in siliceous mudstone during natural in situ combustion of hydrocarbons is attributed to contractile surface forces between mineral grains and an interstitial melt phase. A comparison between bulk density increase during sintering and created fracture space indicates that fracturing resulted from contraction of the rock matrix due to porosity reduction, grain-scale mass transfer, and high-temperature mineral formation. It is suggested that contractile surface forces between mineral grains and between mineral grains and pore fluid contribute to subcritical fracture formation under a wide range of subsurface conditions.