MINDAT.ORG 2018 BENEFIT AUCTION Click here to preview now. Bidding starts June 1st
Log InRegister
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for Educators
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
StatisticsThe ElementsUsersBooks & MagazinesMineral MuseumsMineral Shows & EventsThe Mindat DirectoryDevice Settings
Photo SearchPhoto GalleriesNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day Gallery

Moqui Marble Mysteries

Last Updated: 14th Jan 2013

By Dave Crosby

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 it's 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?

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"?

Article has been viewed at least 8943 times.


Nice article,good clear pictures. Only item I would add is there is no collecting allowed at Big Spencer Flat. It is now part of Grand Staircase-Escalante National Monument. Another look, but don't touch!

Happy Trails,

Jim Gawura
14th Jan 2013 6:12am
Thanks for your comments Jim! I took your suggestion and edited the above.
I had mentioned it on some of the photos, but that won't register with the casual viewer.
Luckily similar concretions have formed in sandstone layers all over the world.
Jan J. van Loef informed me he was studying some from Holland that formed with clay called "Rattle Stones" because of the voids left as water escaped. I sent him 35 specimens of the Moquis and broken shells to add to his studies.

Another thought: Is it possible the layers record in some way the weather cycles as tree rings do?

Dave Crosby
14th Jan 2013 2:30pm
Thanks for the interesting article and photos, and for reminding us that mineral collecting doesn't necesarily have to be limited to crystals!

I think the moquis form by the same process that creates "Liesegang rings" - rhythmic chemical deposition of iron oxides over an expanding front in the porous rock, which probably happens at depth, where there would be no influence from the weather. A worm track, or any other kind of fossil in the sandstone would just end up inside the moqui as the deposition front overtook it, leaving it on the inside.

"Rattle stones", like the ones you mention from Holland, and similar from elsewhere (Iriomote island, for example), form in more smectite-rich rocks when the clay inside the concretion shrinks with dehydration after the weathering out on the surface.

Alfredo Petrov
16th Jan 2013 5:17pm
Thanks for the kind words Alfredo, and the mention of Iriomote Island, Okinawa Prefecture, Japan. I hadn't known that before. The worm by the way appeared to be perfectly fresh when part of the shell broke away to reveal it. It deteriorated quickly once exposed. So much to learn, and so little time!

Dave Crosby
16th Jan 2013 7:50pm
Yes, thanks for the informative article. In addition to those iron-based concretions, I see a many in the southwest U.S. based on calcite. Along the Colorado River in Utah, I once followed a seam of calcite down a sandstone dome "slick-rock" to a low area. At the bottom was a pile of round "marbles".

Here is an article with more fun pictures:

Dean Allum
24th Jan 2013 4:11pm
Thanks Dean, I enjoyed the article. Marjorie is among my favorite geologists. I wonder why she only referred to hematite?
I had the good fortune of communicating with Jan J. van Leof, of Delft,the Netherlands as he retired. I sent him 30 Moqui samples to study along with the "rattlestones" he was examining. He reported that the outer layers have more limonite, the inner layers, practically none. The limonite was almost totally converted to goethite.

Carl Ege of the USGS told me a sample I had given him had a sand grain suspended in the air by a single goethite fiber! He photographed it digitally, then somehow lost the card it was on. Drat! That would have been neat to show!

Dave Crosby
26th Mar 2013 8:40am

In order to leave comments to this article, you must be registered
Mineral and/or Locality  
Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2018, except where stated. Mindat.org relies on the contributions of thousands of members and supporters.
Privacy Policy - Terms & Conditions - Contact Us Current server date and time: May 28, 2018 10:51:15
View slideshow - Go to top of page