Centennial Museum gecko logo

Desert Diary
Fossils/Metamorphic Rock


Rocks are broadly classified as sedimentary, igneous, or metamorphic. Most people understand sedimentary rocks as those made up of small particles derived from earlier rock types, such as sandstone and shale, or chemically precipitated from material dissolved in water, such as some types of limestone. Likewise, igneous rocks are understood as having solidified from a molten state; such things as basalt and granite.

Metamorphic rocks may be a bit more cloudy in the mind of many. "Meta" in this case refers to different, or changed, and "morphic" refers to shape. And sure enough, metamorphic rocks are those that have been changed from what they were originally—changed by the heat and/or the pressure of deep burial within the earth. Thus shale, a sedimentary rock derived from clay, becomes slate; limestone becomes marble; and quartz sandstone turns into quartzite. The commonness of volcanism and geologic upheavals in the Chihuahuan Desert guarantee our possession of metamorphic rocks galore. For folks in the El Paso area, Castner Marble is well exposed on Trans-Mountain Road in our own Franklin Mountains.
pen and ink

Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.


Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.