sandstone - teaching hand specimen of Jurassic fine-grained white Navajo Sandstone, naturally bleached by reducing fluids
The Navajo sandstone ranges from pinkish orange to white. The pinkish color is due to an iron oxide coating on the sand grains. In some areas reducing fluids flowed through the formation, removing the iron oxide coating to produce a white sandstone.
The Navajo was deposited during the Jurassic in an immense coastal and inland dune field, so the sand grains are frosted - they essentially sand blasted each other as they were moved by the wind. The frosted nature of the grains is characteristic of the Navajo and is easily visible under 20x magnification, though a student with sharp eyes can see this with 10x.
The Navajo Sandstone makes up the cross-bedded cliffs at Zion National Park in Utah. Locally it is poorly to moderately well cemented with silica cement. These specimens are moderately cemented and will stand up to student examination, though grains of sand can be rubbed off. Near Hurricane, Utah the Navajo sandstone is 2,400 feet thick.
The sand grains in these specimens are larger than those of a silt and will feel like fine sand to a student. It would be instructive to compare this sandstone with one is larger grained, with one that is cemented with calcium carbonate, and with different colored sandstones, as sandstone has great variety and a student should not see only one example.
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