Earth Notes: Moqui Marbles

Mar 27, 2019

For those who enjoy pleasantly poking around the Colorado Plateau, there’s an endless array of fascinating geologic curiosities. Among them are intriguing stones called Moqui marbles—brownish-black rocks, often roundish but with a variety of fanciful appendages, ranging from pea to grapefruit-size.

Moqui marble
Credit Gary Alpert

In places a profusion of these “marbles” decorate the ground, and their dark colors stand out against the buff-colored sandstone.

Moqui marbles—some call them Kayenta berries or shaman stones—formed deep underground nearly 200 million years ago in Navajo Sandstone. As groundwater flowed through the permeable sandstone, iron minerals were released. Those minerals encased and cemented the sand grains in concentric circles—eventually forming hardened iron concretions. Weathering of the surrounding bedrock exposed the harder, weather-resistant concretions.

Sliced open, each marble reveals a dark outer iron shell and a lighter sandstone filling—kind of like a malted milk ball. Similar gray formations have been discovered on the planet Mars—called Martian blueberries—considered possible evidence for the early presence of water.

Moqui is a Hopi word meaning “dear departed ones.” According to tradition, spirits of the dead play with the marbles at night, leaving them behind to reassure the living that they are happy in the afterlife. Some believe just holding the marbles quietly in the hand has a calming effect.

People seem tempted to gather them. But, many Moqui marbles are on public lands and Native American reservations, so collecting them is strictly prohibited. These marbles should be left on the playing field.