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siltstone - teaching hand specimen of red Triassic siltstone from the Moenkopi Formation

$ 7.50

This siltstone is from the Upper Red Member of the Triassic Moenkopi Formation in Cedar Canyon, Iron County, Utah. The Moenkopi extends throughout the western two-thirds of the Colorado Plateau, with a thick sequence exposed near Cedar City, Utah.

The silt grains in these specimens are smaller than those of a sandstone and and feel gritty when rubbed. They are cemented by silica and iron oxide, so there is no reaction to a drop of dilute hydrochloric acid.

Students should know the sedimentary grain-size progression from mudstone and shale through siltstone, sandstone and conglomerate and be able to make the identifications. They should realize that fine grained sediments are deposited in a low energy environment, either far offshore or in coastal mudflats and in the riverbed and floodplain deposits of slow-moving streams.

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