"Limited temperatures reached by Green River Formation oil shale during surface retorting restrict accompanying mineral reactions to decompositions whose products may have aqueous and gaseous mobility . The substantially higher temperature "" reached during combustion processes in place initiate solid-state mineral reactions . Three solid- state reactions are examined: (1) gas-solid combination retaining sulfur in the shale; (2) solid- solid formation of new minerals; and (3) gas-solid recarbonization. To evaluate the unknown solid- solid reactions the Laramie Energy Research Center conducted tests on two sample representing possible resources for in situ combustion, heating them to temperatures up to 1200oC. new minerals appearing in samples during these experiments were identified by X-ray diffraction. Evaluation of all these solid state reactions indicate that they work to minimize possible environmental consequences of in situ oil-shale development."