In the Listing, Blood of the Living Rocks, we discussed the roll of Iron and it's ability to pigment rock, as well as, the "bleaching" process, as Iron is removed from the rock, with the help of water. In this Listing we will discuss the roll this Iron rich runoff has in forming Concretions, or what is commonly called Moqui Balls or Marbles. But first....
There's a few Rules. Rule # 3: Leave What You Find
*** Please do not remove any of the Moqui Balls from the cache site. Feel free to pick them up and examine them, but put them back where you found them in order for others to enjoy. ***
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Logging Requirements
Email the following information/answers to me:
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In the subject line, please include the following: "Iron Babies, GC3FGA7".
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The number of individuals in your group.
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Find a range of sizes of Moqui Balls and put them in some order, from largest to smallest. Describe their varying degrees of texture and color, along how spherical they are.
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Do the Moqui Balls tend to loose their round shape as they get larger, or get more spherically symmetric, the larger they get?
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Compare the hardness with that of the surrounding sandstone. What do you think happens the hardness of the sandstone as water "bleaches" the Iron from the rock?
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Concretions (Moqui Ball formation)
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The Crimson Source:
Weathering, oxidation and burial, makes the sandstone red. Iron bearing minerals weather and break down, and react with oxygen and water from the atmosphere. The Iron is released and forms a thin film of hematite on the quartz sand grains, giving it a reddish color, depending on the amount of oxidation.
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Bleaching:
Reducing fluid (water), "dissolves" and carries iron, "bleaching" the sandstone. Sandstone is porous, allowing water to move relatively easily through the sandstone, almost like a sponge. Under certain conditions, the Iron pigment bound to the quartz sand crystals will dissolve and be removed from the rock. In some cases, the red pigment (aka hematite) is completely removed, rendering the sandstone a white appearance.
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The Iron Baby:
An influx and mixing with oxidizing fluid causes Iron to precipitate. After the "bleaching" process mentioned above, the Iron is essentially bound to the reducing substance (in this case water), and removes an electron from the dissolved Iron, drastically reducing its solubility. The new Iron precipitates into the spaces between the quartz grains forming concretions. Now instead of the Iron being bound to the quartz sand crystal, it forms a thick "cement", like glue that surrounds the grain.
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This process progresses over millions of years, and the concretions can form many different sizes and shapes. Some of the more unusual concretions form buttons, pipes and columns. Although the concentrated hematite appears to be black in reflected sunlight, it still retains its red color when viewed under a microscope.
The round shape of the concretions found at White Pockets is the most common shape seen, and it is not known why this is so. It might be that some "seed" changes the local chemistry that allows the precipitated Iron to form in such uniform spherical shapes.
References and further reading:
"Rainbow of Rocks", by Marjorie A. Chan and William T. Parry; Department of Geology and Geophysics, 135 S. 1460 E. University of Utah, Salt Lake City, UT 84112-0111. Public Information Series 77; Utah Geologic Survey, a division of Department of Natural Resources
"Scenes of the Plateau Lands and How They Came to Be", William Lee Stokes; 1969, 20th printing. Starstone Publishing Company, 333 J Street, Salt Lake City, UT 84103.
Biek, B., 2002, Concretions and Nodules in North Dakota North Dakota Geological Survey, Bismark, North Dakota.
Epoch Times Staff, 2007, Mysterious Huge Stone Eggs Discovered in Hunan Province Epoch Times International. Photographs of large cannonballconcretions recently found in Hunan Province, China.