= Solution
Within a shallow <fault zone> undergoing <brittle fracture>, repeated sliding crushes and grinds grains. Expect <fault gouge>, potentially rich in fine <clay minerals>, and coarser angular <fault breccia>; a cohesive, cemented crushed rock is a <cataclasite>. <Slickensides> or displaced grains can record the sliding direction.
An opening <geological joint> need not contain any <fault rock>: it may be an open crack. If fluids circulated, it can contain a <mineral vein>, for example <calcite> or <quartz>, grown from the fracture walls. Thus \b[comminuted <fault rock> supports shear, while open space or a crack-filling <mineral vein> supports opening]. Mineral filling is conditional on fluid chemistry and timing; its precise composition cannot be inferred from the photograph.
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