Monday, January 6, 2014

Liesegangen Banding In The Navajo Sandstone

An interesting feature of the Navajo Sandstone is the presence of Liesegangen banding, those ribbons of rustiness that swirl and whirl so dramatically across often vast expanses of rock. 

Mr. Ben, Liesegangen banding, and the Navajo Sandstone

Liesegangen banding (and rings, too) are believed to form in sedimentary rocks such as the Navajo Sandstone when groundwater saturated with iron minerals moves through the pore spaces between the sand grains.

To picture this scenario, consider dripping water moving slowly through marbles in a jar – there is a whole lot of empty space for that water to work its way through those marbles. 

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Cindy (r) and yours truly, surrounded by whirling and swirling

In order for the Liesegangen bands or rings to actually form, an iron molecule would need to precipitate out of solution and form a “seed” crystal in one of these tiny pore spaces (“seeds” are how mineral crystals of all sorts are usually formed, from quartz to calcite). If the groundwater is supersaturated with enough iron, then the crystals will be able to grow – as long as there is enough room in the pore space to let them. 

IMG_6024 Liesegangen Banding
Liesegangen banding in the Navajo Sandstone near Yant Flat
It is after this initial crystal growth into the surrounding pore spaces and after chemical separation of the iron minerals from the water that the bands, or rings, develop. 

Shadows crossing the Navajo Sandstone

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Whirling and swirling iron banding accents the Navajo Sandstone

If these color bands or rings were caused by groundwater flowing along the original bedding then the bands accentuate the bedforms. However, the flowing, sinuous patterns of the Liesegangen bands and rings more often cut across bedding planes in these sedimentary rocks, going wherever the porosity of the sandstone takes them. 

Cindy is belting out a geologic show tune behind me!

I can think of far worse things to be doing in this life than to be spending an entire day hiking around Yant Flat in southwest Utah with two good friends while we investigate Liesegangen bands (oh, poor me!). Mr. Ben and I jabbered on for hours, figuring out the geochemistry while his wife Cindy enthusiastically belted out gospel hymns and show tunes with geologic themes. 

IMG_6047 Liesegangen Bands
Liesegangen banding, up close and personal

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