About one year ago, I sent an article on Martian spheres (note 1) to an American expert on ooids. He replied: “If the spheres contain iron oxide, the spheres may be Moqui marbles.” Anyway, Moqui marbles were formed by microbes, as evidenced in this article:http://research.unl.edu/annualreport/2013/microbes-and-moqui-marbles/ (note 2)
Note 1: see the article “Putative Martian Microbes Formed Plentiful Ooids on Mars” at https://www.esciencecentral.org/journals/putative-martian-microbes-formed-plentiful-ooids-on-mars-2332-2519-1000150.php?aid=71892 Note 2: Quote from the link: “Microbes helped form Moqui marbles, unusual balls of rock found in southwestern U.S. sandstone, roughly 2 million years ago. That discovery by UNL geomicrobiologist Karrie Weber and colleagues has implications for finding life on Mars and for better understanding Earth’s past. Moqui marbles have a soft, sandy interior and a hard, round shell made of iron oxide. Weber learned that microorganisms feeding on a mineral rich in iron carbonate began the process that created the marbles, which range in size from BBs to cannonballs. Knowing that life could persist in this type of rocky, iron-rich environment provides a guide for searching for life elsewhere on Earth, or even on Mars, where similar structures have been found.”