Mystery object

I’m sure someone will know what these are. The halves are heavier than they look and fit together to form an imperfect sphere. The whole thing looks like a petrified walnut as the two halves fit together. The smaller globe is stuck inside the larger “shell”. The objects appear to be sandstone of some type (sandstone is abundant at Pearl Creek Farm) and I’m pretty sure they’re natural but not biological in nature. They were found near the creek and we find them or something similar occasionally, sometimes not broken apart. Any guesses?

Mystery objects
Mystery objects

Of course, the answer came quickly. Here’s more information from John Oliver:

Look up moqui marbles or moqui balls (also spelled “mokee and moki.”
The iron oxide concretions exhibit a wide variety of sizes and shapes. Their shape ranges from spheres to discs; buttons; spiked balls; cylindrical hollow pipe-like forms; and other o
dd shapes. 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. The surface of these spherical concretions can range from being very rough to quite smooth. Some of the concretions are grooved spheres with ridges around their circumference.

They consist of sandstone cemented together by hematite (Fe2O3), and goethite (FeOOH). The iron forming these concretions came from the break down of iron-bearing silicate minerals by weathering to form iron oxide coatings on other grains. During later diagenesis of the Sandstone while deeply buried, reducing fluids, likely hydrocarbons, dissolved these coatings. When the reducing fluids containing dissolved iron mixed with oxidizing groundwater, they and the dissolved iron were oxidized. This caused the iron to precipitate out as hematite and goethite to form the innumerable concretions found in many Sandstones.