Liesegang blocks from sandstone beds of the Hojedk Formation, Kerman, Iran

Three types of Liesegang blocks (sandstone blocks with Liesegang patterns) are present in sandstone beds of the Hojedk Formation near Sowlat Abad, located in the Kerman Province of Iran. The Liesegang blocks are mostly 6 to 12 cm by 4 to 8 cm in area, in beds with a mean thickness of 10 cm. The Liesegang blocks are best developed along the drainages and vanish laterally to the sides and vertically beneath. They are formed in sandstone blocks bound by the tectonically induced joints and fractures at the periphery, and the bedding plane at the bottom. Each Liesegang block is composed of a core, and alternating iron-poor shells (intermediate shells) and iron-rich shells (‘iron’ shells). The shells follow the configuration of the outer shape of the block. The most important factors involved in transformation of a sandstone bed into Liesegang blocks are: a condensed grid of joint polygons, surface water, the appropriate topographic site of exposure, and the composition and thickness of the sandstone bed. Microscopic studies, and the study of gains and losses of elements suggest two opposing diffusion direction trends in the course of Liesegang block formation. The effect of Recent tectonic movements on the Liesegang blocks manifested itself in various forms. Of interest, is partial replacement of the earlier Liesegang patterns by the later patterns along joints, and formation of compound Liesegang blocks (Liesegang blocks with more than one set of Liesegang patterns). From the study of Liesegang patterns within the compound Liesegang blocks, the configuration of the joint polygon related to each Liesegang pattern, and thereby the sense of stress field migration in the area, can be deduced.