Rocks in Kansas

Of the three types of rock—sedimentary, igneous, and metamorphic—the vast majority at or near the surface in Kansas are sedimentary.

Igneous rocks are formed from hot molten magma that pushes up toward the surface from Earth’s interior. Metamorphic rocks are altered from existing rock through heat, pressure, and chemical processes. Sedimentary rocks most often form when sediment and pieces eroded off other rocks are buried then pressed and cemented together. However, they also may form from chemical sediment that settles out of water or the remains of plants and animal.

Sedimentary rocks are laid down in layers called beds, often one on top of another. Pieces of limestone, shale, and sandstone small enough to hold are debris broken off layers of rock exposed at the surface.

In Kansas, sediment in sedimentary rocks was first deposited along shorelines or the floors of seas, deltas, or swamps that covered parts of the state off and on for millions of years—up until about 65 million years ago. After a layer of sediment dried, it eventually was buried under younger layers. As the weight from the overlying sediment increased, lower layers were pressed and cemented into solid rock over time. Depending on the type of sediment deposited, different rocks formed—limestone mainly from the mineral calcite that precipitated from water, sandstone mainly from sand, and shale mainly from clay.

Not all rocks found in Kansas formed there. Unusual rocks that were carried or dropped into the state from other places include layers of volcanic ash carried hundreds of miles by the wind, quartzite boulders dragged in by vast sheets of glacial ice, and meteorites that plunged in from outer space.