Most commonly known as Moqui marbles, these little brownish-black balls are composed of iron oxide and sandstone. According to the Utah Geological Survey, these “blackberries” were formed underground with the help of iron minerals and flowing groundwater.
Utah researchers say this combination occurs in multiple places throughout Southern Utah near outcrops of Jurassic-age Navajo Sandstone.
Officials say the word “Moqui” comes from the Hopi Tribe.
“The Hopi were previously known as the Moqui Indians, named so by the early Spaniards, until their name was officially changed to Hopi in the early 1900s,” UGS details.
According the Utah Geological Survey and some internet sources, there is a Hopi legend that the Hopi ancestors’ spirits return to Earth in the evenings to play marble games with these Martian-like blackberries. Then in the mornings, the spirits leave the marbles behind to reassure their relatives that they are happy and content.
“Moqui marbles, sometimes spelled Moki, are also known by collectors by many other names—Navajo cherries, Navajo berries, Kayenta berries, Entrada berries, Hopi marbles, Moqui balls, or Shaman stones. Geologists call them iron concretions,” shares the Utah Geological Survey.
Utah Geologists say these balls of iron concretions typically range in size from a fraction of an inch to several inches in diameter — so from the size of a pea all the way to the size of a large grapefruit.
Officials say in addition to marbles or balls, these iron concretions can also be found in shapes similar to buttons, pipes, corrugated sheets, “flying saucers,” and plates.
“The host rock for the marbles, the Navajo Sandstone, was originally deposited around 180 to 190 million years ago as a huge sand dune field, similar to the modern Sahara, that covered parts of Utah, Arizona, Colorado, Wyoming, Idaho, Nevada, and New Mexico,” UGS states. “A very thin, microscopic layer of hematite (an iron oxide mineral) coated the sand grains, giving the sand its red color. The sand was later buried by other sediments and eventually cemented into sandstone, during which time the hematite coatings continued to spread over the grains, ultimately giving us some of the most spectacular red sandstones visible in Southern Utah.”
Now Utah is not the only place where these bizarre balls are found. According to the Utah Geological Survey, similar balls exist on the planet of Mars, where they are officially known by geologists as Martian blueberries.
“Discovered on Mars by NASA’s Mars Exploration Rover Opportunity in 2004, the Martian blueberries are thought to have formed in a similar manner to the Moqui marbles on Earth, therefore providing some of the first evidence for water in Mars’ ancient past,” they add. “And just like on Earth, these hematite concretions were found scattered on the ground and embedded in rock outcrops, ‘like blueberries in a muffin,’ according to one rover scientist.”
According to the Utah Geological Survey, Martian blueberries are also not blue, but gray. They are also much smaller than most marbles in Utah, usually about BB pellet-size.
“By continuing to study iron concretions in Utah, geologists can make analogies as to how these blueberries formed on Mars,” UGS concludes.