Morton Gneiss

This is – and probably will remain – the oldest rock in our Crossroads collection. This Morton Gneiss rock is ~ 3.5 billion years old.

Consider for a moment:

• the Earth is 4.6 billion years old
• the oldest rock on Earth is Lunar sample 67215, dated 4.46 billion years old (Apollo 16 mission)
• the oldest (arguably) dated surface rock on Earth is 4.03 billion years old (Canadian Shield)
• the oldest rock formation, known as banded iron, is 3.7 billion years old
• the oldest rock in Fremont County is 1.7 billion years old

This Morton Gneiss is a rock with a long story to tell. Some very old rocks can tell us how much oxygen there was (or wasn’t) in the atmosphere or oceans at a particular time in Earth’s history.

Gneiss (pronounced ‘nice’) is a type of rock that is extremely deformed because it has been buried so deep and for so long that the high temperature and pressure have totally transformed the rock from whatever it was before into a new rock. Most gneiss can be identified by its banding (aka foliation), stripes or layers of darker and lighter colored bands. Much of the Royal Gorge is gneiss. The cutting of the gorge allows us to see this highly metamorphosed rock in place.

For those interested in a more ‘geological’ description of the Morton Gneiss: this Archean crystalline basement rock from the Minnesota River valley in southern-central Minnesota is the oldest whole-rock continental crust in the US. (Archean is the oldest Eon in Geology. Basement rock is the thick foundation of ancient rocks that form the crust of the continents.)

Not only is the Morton Gneiss ancient, but it has a beauty that puts it in high demand as an ornamental stone for buildings and monuments. The colors come from different minerals: quartz (white), pink feldspar (pink), gray feldspar (gray), biotite (shiny black mica), and amphibole (needle-like black crystal).

This rock was provided by James and Susie Aber, recently retired geology professors from Emporia State University in Kansas. In early 2018, Jim and Susie visited the Geology Time Trail, offering muchappreciated suggestions for improving the trail, ranging from protection of rocks to additional geologic information about various rocks along the trail.

As this rock is small and requires special protection, it will reside in a display case near the Geology Lab inside Pueblo Community College – Fremont Campus, and not outside along the Geology Time Trail.

To view the rock, please visit the PCC website for open hours: http://www.pueblocc.edu/fremont/
More information on the Morton Gneiss can be found at: http://www.mnopedia.org/thing/morton-gneiss