Greetings!
Here is an awesome article all about Moqui Marbles written by Dave Crosby and origionally published on Mindat.org January 14th, 2013.
Goethite in the Navajo Sandstone has created a mystery. How and Why does it form spherical layers?
These iron (limonite exteriors, goethite interiors, sand centers) concretions are known as Moqui (Now known as Hopi) Marbles. The Navajo Sandstone is about 2,000 feet thick and was deposited during a very dry period 175-190 million years ago.Take an eight ounce glass and fill it with dry sand. Now, with a measuring cup, fill it with water. Amazing?
Sandstone basins serve as huge sandy seas. They can expel prodigious amounts of water at their margins.
In wet environments iron hydrates to limonite that floats through the sand grains until the water leaves it deposited somewhere surrounding sand grains. As drying continues, limonite crystallizes as goethite. As the water is expelled, limonite/goethite is deposited on its Chanel walls. Another wet season, another layer of limonite/goethite. Notice that the Moqui center above consists of three concentric shells of goethite coated sand grains with uncoated grains between. The Mysteries are: Why spheres in the first place, then why the small, then huge gaps between the different groups of layers? (to see the photographs visit the article page here...)
My conclusion: Like people on a subway platform, limonite blobs like their space, at first staying as far as possible from each other, then slowly newcomers fill the space in between. PERHAPS close wet cycles bring new layers of limonite that deposits a sand grain away from the limonite that has now turned to goethite. Some kind of magnetic or piezoelectric effect?Again, PERHAPS long drying cycles allows more goethite formation and a greater repulsion. Growing spheres make contact with surrounding spheres that join together to form a much larger sphere, encompassing and protecting the enclosed sand from further moisture entrance.
That is my guess. What is yours?
Jim Gawura is correct. as I mentioned on some of the photos above, the weather takes the Moquis all the time. We, according to the government, now should not.
More mysteries: How did an earthworm get entombed in a Moqui, and how long ago? 180 million years? What stopped water flow to the tops of some Moquis, preventing further growth? Why are some so misshapen, while most are nearly perfectly round? Why are some
restricted at their circumference while others expand into "flying saucers"?
References:
http://en.wikisource.org/wiki/Popular_Science_Monthly/
Volume_5/July_1874/The_Moquis_Indians_of_Arizona
Special thanks to Dave for letting us use this article in our newsletter!
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