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University of Missouri Department of Geological Sciences

Rock type:      Lamprophyre
Location:        Trinidad, CO

This rock contains two different rock types. Most of it is an unusual type of basaltic magma, rich in

water and potassium, called lamprophyre. Stuck to the edges of the intruding sheet of lamprophyric

magma are pieces of coal, which got baked by the heat. On cooling, the coal has shrunk and

cracked into polygonal columns a little like the Devil’s Honeycomb, but on a much smaller scale.

This magma sheet is about 5 feet thick and weathers orange. The surrounding coal and shale

beds are mostly grey and crumbly, forming slopes rather than small cliffs. The magma is mid-

Tertiary in age, around 30-20 million years old, and it intruded into uppermost Cretaceous

coals that were laid down only shortly before the asteroid impact that ended the reign of

dinosaurs and the Mesozoic Era.

Photo by Alan Whittington, MU Geology

Resources:

US Geological Survey online guide to the continental Cretaceous-Tertiary boundary in the

Raton basin, Colorado and New Mexico:
http://esp.cr.usgs.gov/info/kt/intro.html

MU Geology Department
http://geology.missouri.edu/