Moqui Marbles are geological formations, known to scientists as iron oxide concretions, found primarily in the desert landscape of the Southwestern United States. They are small, spherical to disc-shaped mineral balls composed of a hard shell of hematite surrounding a core of sandstone. These distinct, brownish-black objects range widely in size, from that of a pea to several inches in diameter, and are sought after by collectors for their unusual form.
The Geology Behind Moqui Marbles
The formation of Moqui Marbles is tied to the Jurassic-age Navajo Sandstone, the host rock underlying the region. This sandstone, originally a vast system of ancient sand dunes, contained trace amounts of hematite. The concretions themselves are much younger, forming within the last 25 million years as the result of groundwater activity.
Water containing dissolved iron traveled through the porous sandstone. When this iron-rich water encountered a change in chemical conditions, the iron minerals precipitated around a nucleus of sand grains. This process, known as concretion, created a concentric layering of iron oxide, forming the hard, protective shell that gives the marble its durability. The marbles become visible when the softer, surrounding sandstone erodes away, leaving the weather-resistant iron balls scattered on the surface.
Primary Geographic Regions for Discovery
The search for Moqui Marbles begins by locating extensive exposures of the Navajo Sandstone formation across the Colorado Plateau. The primary region for discovery is Southern Utah and Northern Arizona, specifically in areas outside of protected parklands. While they are found in places like Zion National Park, collecting in all National Parks and Monuments is strictly forbidden.
Focusing your search on Bureau of Land Management (BLM) lands adjacent to these areas is the most practical approach for legal collection. Large tracts of BLM land in counties like Kane and Garfield in Utah, or the Paria Plateau in Arizona, feature the necessary geological conditions. Marbles are found in the sediment that accumulates at the base of eroding sandstone cliffs and slopes.
Ethical Collection and Legal Restrictions
Collecting Moqui Marbles requires a clear understanding of land ownership and adherence to specific regulations. Collection is strictly prohibited within the boundaries of all U.S. National Parks, National Monuments, and on tribal lands. It is necessary to confirm land status before beginning any search.
On most Bureau of Land Management (BLM) acreage, casual collection of rocks and minerals for personal, non-commercial use is generally permitted without a special permit. The BLM defines this casual collection as a reasonable amount, typically limited to 25 pounds per day, plus one piece, with a total annual limit of 250 pounds. Collectors must only use hand tools, and any surface disturbance must be negligible, meaning no significant digging or excavation is allowed. If you are collecting on State Trust Lands, a rockhounding permit is typically required.
Field Guide: Identifying and Locating Marbles
Identifying Moqui Marbles in the field is straightforward due to their distinctive coloration and shape. They appear as dark, chocolate-brown to black spheres, ovoids, or discs, contrasting sharply with the pale tan or white color of the eroding sandstone. The surface is often dull and rough, though some specimens are naturally polished or have subtle ridges.
The most effective way to locate them is by searching “puddles” of accumulated sand and sediment at the base of Navajo Sandstone outcrops. As the softer rock disintegrates, the hard, dense iron concretions roll downhill and gather in groups. Searching after a period of rain can make them easier to spot, as moisture darkens the iron oxide shell, increasing the contrast. Look for areas where the sandstone is visibly crumbly or actively eroding, as this is where new marbles are exposed.