sandstone showing Liesegang banding - teaching hand specimen of Liesegang-banded sandstone from the Chinle Formation
This sandstone forms a prominent cuesta on the flanks of the Virgin Anticline near Hurricane, Utah. These specimens are from the Shinarump Conglomerate Member of the Chinle Formation, Late Triassic in age, and are from a channel sandstone facies in the Shinarump. The cement is silica and iron-oxide - these specimens will stand up well to student examination.
Liesegang banding is formed of sinuous bands of iron-oxide cement alternating with iron-oxide staining. The area between iron-oxide cement bands regularly varies between lightly stained rock and rock that lacks iron-oxide staining. The banding crosscuts and obscures sedimentary structures. The iron-oxide staining consists of mounds of acicular needles precipitated on quartz grains.
The pore-filling cement consists of both needles and hexagonal plates of iron-oxide with a morphology similar to that of the microaerophilic iron-oxidizing bacteria Gallionella. The iron-oxide cement appears to be produced by microbially-mediated dissolution of siderite (iron carbonate) and oxidation of ferrous iron and is the result of the geochemical drive for organization combined with microbial activity.
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