Brittle fracturing in rocks is a progressive process involving changes in stress, strain, and porosity. Changes in these properties occur heterogeneously within a rock, and are manifest at the grain scale, which is difficult to observe directly in the laboratory or the field. This study uses the discrete element method (DEM) to show that fractures correspond to zones of generally lower stresses, higher porosity, and highly localized dilation and distortional strain. Using the DEM, we conducted numerical biaxial experiments at different confining pressures to probe the internal conditions of a sandstone numerical analog. When compression begins, the stresses within the sandstone are relatively homogeneous with anastomosing stress chains. At yield stress, when the confining pressure is relatively low, multiple dilational bands start to open. At peak stress, high magnitude stress chains localize adjacent to the developing shear band and distortion is evident. Post peak stress, through-going shear fractures are fully developed. High stresses are transmitted across the fracture where porosity is low through a network of particles in contact. With increasing confining pressure, distortion is favored over dilation during deformation, Also, the number of particles that define the width of a stress chain across a shear fracture, and the steepness of the fracture increases. Our results can be applied to understanding stress conditions of field samples, and in constraining rock property changes during reservoir modeling of fractured reservoirs.