MINERAL OF THE MONTH: June 2012 – Moqui Marbles


The mineral of the month for this update is an unusual type of iron concretion called Moqui Marbles. These round rocks form in the Navajo Sandstone formations spread across northern Arizona, northwest Colorado, and Utah. Most are found in the numerous national parks in the area, so they can no longer be collected. I recently purchased a large quantity of moqui marbles that were collected legally many decades ago.


The wide range of colors exhibited by the Navajo Sandstone reflect alteration by groundwater fluids over the last 190 million years. The different colors are caused by the presence of varying mixtures and amounts of iron minerals such as hematite, goethite, and limonite. These minerals fill the pore spaces between grains of sand, causing the variation in colors in the sedimentary layers. The iron in these strata originally arrived via the erosion of iron-bearing silicate minerals. Variations in the type and proportions of precipitated iron oxides resulted in the different crimson, vermillion, orange, salmon, peach, pink, gold, and yellow colors of the Navajo Sandstone.

The Navajo Sandstone is also well known for its iron concretions. They are believed to represent an extension of Hopi Native American traditions regarding ancestor worship (“moqui” translates to “the dead” in the Hopi language). Informally, they are called “Moqui marbles” after the local proposed Moqui native American tribe. Thousands of these concretions weather out of outcrops of the Navajo Sandstone within south-central and southeastern Utah within an area extending from Zion National Park eastward to Arches and Canyonland national parks. They are quite abundant within Grand Staircase-Escalante National Monument. The Utah concretions formed around 25 million years ago when minerals precipitated from groundwater flowing through much older Navajo sandstone.

The iron oxide concretions found in the Navajo Sandstone exhibit a wide variety of sizes and shapes including discs, buttons, spiked balls, hollow pipes, round spheres, and others. Although many of these concretions are fused together like soap bubbles, many more also occur as isolated concretions, which range in diameter from the size of peas to baseballs.


These concretions are regarded as terrestrial analogues of the hematite spherules, called Martian “blueberries” or more technically Martian spherules, which the Opportunity Rover found on Mars.

Many people like to buy Moqui Marbles in pairs. The “male” spheres have ridges whereas the “female” spheres are smoother. Used together they balance the masculine and feminine energies. They are believed to be among the most energetic stones on earth. Their major properties are claimed to be cleansing, relaxation, and they provide a great boost to meditation.

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