Game of stones
Moqui marbles on a sandstone slope. A new study reveals that the moqui marbles are less than 25 million years old.
The unusual geologic formations are concretions — sandstone balls cemented by a hard shell of iron oxide minerals.
Millions of years in the past, a mixture of water and natural gas flowed through the Navajo Sandstone, bleaching the rocks from red to creamy white. The stolen iron became the moqui marbles.
At Checkerboard Mesa in Zion National Park, the Navajo Sandstone is creamy white.
The lower levels of Navajo Sandstone at Zion are stunning red, orange and peach colors.
Field of dreams
The concretions collect in topographic lows.
Moqui marbles come in many shapes and sizes.
Resistant iron minerals erode more slowly than the softer sandstone.
Lumps and bumps
The spheres grew layer by layer, making contact with others nearby until many spheres became one large ball.
Wind-blown sand polishes the outer shell of hematite or goethite.
Moqui marbles emerge from cream-colored Navajo sandstone.
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