Touching a Piece of Geologic Time

This week, Local Time welcomes guest writer Sherrie Horn, who shares her experience with a unique student program.

Volunteer naturalist Bob Hickey, from Colorado Parks and Wildlifes Mueller State Park, came to my charter school, Academy for Advanced and Creative Learning  (a free charter public school in Colorado Springs District 11 that specializes in gifted education) to present a touch-table format talk displaying and explaining regional rocks. My students learned first-hand all about local geology and the earth’s formation.

Besides pure minerals, three different types of rocks make up the majority Earth’s crust. Mr. Hickey showed the students all three types of rocks: igneous, sedimentary, and metamorphic. Igneous rocks occur in both intrusive (under the earth’s surface) and extrusive (on the earth’s surface) forms. They cool at much different rates and look different, especially up close. It was fascinating to touch an intrusive granite and an extrusive rhyolite and see the different sizes of particles that comprised each one, which is why Bob Hickey travels to schools to share his rock samples and experience with kids.

Light igneous rocks. Extrusive rhyolite (left), and intrusive granite (right). (Photo Credit: Sherrie Horn)

Mr. Hickey explained, “Intrusive magma forms the mantle that is trapped in the earth’s crust then cools slowly, growing large crystals. It never makes it to the surface. The word ‘igneous’ comes from the Latin word for fire. Hence, igneous rocks are referred to as ‘fire rock’ because they form from hot molten magma deep down in Earth’s mantle, then make their way into Earth’s crust where they either stay inside or extrude out to the surface to cool. Igneous rocks are the primary composition of Earth’s crust and they were the first rocks to form from the cooling magma when Earth originally solidified. The mineral crystals in igneous rocks are randomly ordered due to the inconsistent mixing of the minerals in magma. Three types of igneous rocks based on minerals make up each kind: heavy (mafic), light (felsic), and a mixture of the two (intermediate).” One student questioned the boring names of the categories of igneous rocks. “When scientists named these types of rocks, why weren’t they more creative?”

Mr. Hickey brought in several examples of minerals in igneous rocks such as hornblend (my favorite, because it shares my name), granite, gabbro, rhyolite, feldspar and trachyte. I was excited to learn that Pikes-Peak-area granite feldspar has potassium in it which ranges in color from orange, to pink, to tan, to cream. A fine example of this pink granite can be found at the Broadmoor Hotel (founded by Spencer Penrose). The grand central staircase was constructed entirely of this granite, specifically because its color can be found nowhere else on Earth. Feldspar from the Mt. Antero and Salida area, on the other hand, has sodium instead, and forms into volcanic trachyte, which is white or cream colored. Students commented, “It looks just like the granite has the measles. It’s all blotchy,” and “The lavender granite looks just like a bath bomb. It is lavender with specks in it.”

Trachyte extrusive (left) and syenite intrusive (right) light igneous rock. (Credit: Sherrie Horn.)

The second type of rock Mr. Hickey showed the students was sedimentary rock. Sedimentary rocks form from cementation of sediment created by erosion due to wind, water, glaciation and ice. Interestingly, 75 percent of the outside layer that we see of Earth’s crust is covered by sedimentary rock, but only five percent of the entire crust is sedimentary. Sandstone, a type of sedimentary rock, is pink in color and can be seen all over the state, which is one of the reasons Colorado got its name (“colorado” is Spanish for “the color red.”) Sandstone is fragile and easily eroded by Colorado’s harsh winters and violent winds. Some of the samples the students held were breccia, chert, limestone, shale and sandstone.

The strongest and, in my opinion, most beautiful type of rock is metamorphic rock. Metamorphic rock started off as either sedimentary, igneous or previously metamorphosed rock, but was subject to immense heat and pressure. Glass blowers do the same type of thing when they re-heat and re-form a piece of glass artwork by adding minerals to change color. Some of the sample metamorphic rocks Mr. Hickey shared with us were banded and folded gneiss, marble, schist, slate, phylite and meta-quartzite.

We are so fortunate to see all three types of rock as we explore Colorado, because our state is one of the only places where 25 percent of the Earth’s crust has exposed igneous rock. Plate tectonics caused the formation of different rock types millions of years ago, and erosion and weather have taken it from there. So when you’re hiking, look around at the amazing, unique geological landscape we share in this beautiful state.

Mueller State Park’s environmental education programs are an exciting and fun way to engage students in the world around them. Through science-based exploration and hands-on activities, students gain a deeper understanding of the natural world. Mueller State Park makes a great outdoor classroom with a healthy montane ecosystem and abundant wildlife. Mr. Hickey says, “Mueller State Park and I are very interested in supporting our schools with programs both at the schools and at the park.  Our Park Program Coordinator, Linda Groat, is in charge of booking and arranging support for school programs.”

These programs address Colorado Academic Standards, and custom-designed programs are available upon request. Although some programs are best experienced in the park, others may come to your school. There is no fee for any program; the only cost is the State Park entrance fee of $7 per vehicle for a day pass or a $70 annual pass for cars or buses. To schedule a program, contact Linda Groat at (719) 687-2366 ext. 107 or email Mueller State Park can be found at 21045 Highway 67 South, Divide, CO 80814-0039. The park is open year round, and the office and visitor center are open from 9 am to 5 pm in the summer.


Sherrie Horn was raised in Southern California and served for over 20 years in the US Air Force. She completed her Master’s degree in education at the University of Northern Colorado in 2014 and works as a middle school gifted education teacher at Academy ACL in Colorado Springs.  Her interests include photography, scrapbooking, camping, hiking and anything outdoors. And baby goats.

Photo By: Sherrie Horn (Bob Hickey holding a piece of schist).