| Summary: | New method of drilling narrow vertical boreholes by controlling hydrogen combustion assumes that rocks melt and radial fractures
are formed within the rock under high temperatures and pressures at the interaction of the rock and the flame. To verify the range of formed
radial fractures in different rock types, it is needed to know in detail rock and mineral properties before and after melting process of the
rock(s). Rocks extend due to the heat and contract with cold. As the rocks consist of minerals with different thermal expansion, the rock
extension and contraction differs in different directions. Temperature changes cause the stress between mineral grains, resulting in
microfracture formations. Rock samples of granite, andesite and sandstone were pounded into fraction less than 10 microm, melted and cooled under
specific conditions, and analysed using REM and EDAX. Cooled granite melt contains shear fractures evolved across the sample due to
the tensile stress in the quartz grains occurring in pounded sample. No fractures were observed in cooled melt of andesite. Cooling of melted
sandstone grains resulted in evolution of highly porous material with no microfractures.
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