Rocks and Minerals: The Oldest Storytellers

Nobody explains Colorado’s rockstars better than James Hagadorn, Ph.D., my favorite scientist at the Denver  Museum of Nature & Science. Colorado’s geological features wouldn’t be near as fabulous without all the amazing supervolcanoes.  I found Dr. Hagadorn’s description of them to be the best.

 “Colorado’s got a  ton of volcanoes. One of ’em blasted out the biggest eruption in all of Earth history. Others produced some of our most important diamond, gold and fossil deposits. If you imagine the Earth as a giant avocado, Earth’s “pit” is a radioactive core of ultra-hot metal. It’s surrounded by a hot gooey layer called the mantle (the guacamole ingredient). We live on the skin of the avocado—perched on tectonic plates that cruise around atop the mantle like bumper cars. Where plates collide, one of them often gets shoved down toward the mantle, where it sweats out water and many of its gases. These cause nearby rock to melt into magma,  which then burbles upward toward the surface. This process has happened many times beneath Colorado. 

The  Dotsero Crater is a ½ mile wide, ¼ mile deep volcano located a mile north of  I-70 east of Dotsero. It is Colorado’s youngest volcano.
 

Depending on its chemistry, magma erupts in two main forms—oozing or explosive. Lava that oozes out gently forms a rock called basalt, thick flows of which cool slowly and develop dramatic vertical columns (think: Devil’s Tower). Colorado’s Flat  Tops are a great example—they’re frosted with so much basalt that they don’t have jagged peaks like the rest of the Rockies. When the blend of volatile gases and water is just right, magma blasts upward and outward as ash and vapor,  forming slippery soils and muds like those near Silverton, Creede, and Del  Norte. 

Perhaps Colorado’s coolest volcano is northwest of Fort Collins, where there’s a  10-mile-wide ring representing a remnant volcanic neck. This so-called kimberlite pipe is so prominent you can see it from outer space. What’s unique about it is that it carried diamonds from the mantle up to the surface—making  Colorado one of only two states that are rich in diamonds (the other is  Arkansas). 

The easiest belch of a volcano for Front Rangers to ogle is the one that produced  North and South Table Mountain. These flat-topped mesas formed as lava spurted from the Ralston Dike about 2 miles northwest of N. Table Mountain, filling in local valleys and streams with a lake of lava. This volcanic vent erupted at least four different times, about 60 million years ago. Fast forward to today,  and the softer strata that surrounded these valley-filling flows have eroded away—leaving the resistant caps of fossil lava behind. To see these up close,  drive Highway 58 between Wheat Ridge and Golden. Or better yet, hike to the top of its volcano-scape, starting at the Table Mountain Trailhead off Highway  93. 

Colorado’s most famous volcanoes erupted about 35 million years ago, destroying nearly all life in the region and producing two gigantic Pompeii-like deposits. At  Florissant, about 60 miles west of Colorado Springs, ash eruptions and ash avalanches dammed a nearby river. The water backed up, creating a huge lake in which animals and plants were frequently buried. The fine ash helped to preserve delicate fossils like leaves and insects; it even entombed a grove of giant sequoia trees. Check them out in Florissant National Monument, or if you’d like to collect, stop by the “pay-to-dig” in town. 

About  100 miles southwest of the Springs is the big kahuna of volcanoes—the San Juan  Volcanic Field. It is so immense it’s hard to fathom. Among its many eruptions was one that expelled nearly 5,000 times the amount of material produced by  Mount St. Helens. Enough debris was ejected to cover the state with a  six-inch-thick blanket of hot ash. This killed many plants and animals and contaminated the air so much that sunlight would have been blocked enough to reduce temperatures by one to three degrees for quite a while. Glad we missed that one. 

Although the last eruption in the San Juans was 30 million years ago, the earth is still hot below the surface. Water percolating down and back up again produces many of the area’s hot springs—Mount Princeton and Conundrum among them. Our cutest volcano erupted a mere 4,100 years ago. Look for it next time you’re driving west on I-70, about a mile before you hit Dotsero. On your right is the reddish-brown edge of the half-mile-wide crater. On your left is the lava flow that flowed southward from the crater and dammed the Eagle River. The resulting basalt and its frothy cousin, scoria, is currently being mined for landscape stone. The  Rockies are still volcanically active—witness the supervolcano that burbles beneath Yellowstone. But not to worry—seismic (earthquake-monitoring) networks will give us plenty of time to leave the blast zone beforehand. So if you dig volcanoes and a trip to Hawaii isn’t in the budget, perhaps take a  road trip this summer. Visit some of our very own, and very awesome,  volcanoes.”

  A rock = a concretion. It will be solid, and the inside of the rock will look like the outside. Fossil bone, on the other hand, will probably preserve the internal bone structure.

After Dave and I came home after a winter's walk-up Dinosaur Ridge, I came home to read about the incredible digs and finds near where I live.  I remembered a couple of presumably fossil bones within my most cherished rock collection. I almost forgot about them, but when I looked, I had to question if they were real or not. If you like me, try to figure things out. 

The three-question rule for junior rock detectives might apply when trying to distinguish rock and fossil bone.

• A. The location? From where did the presumed fossil bone come?
• B. The look? Check out every aspect; a rock will look the same inside and out.
• C. The tongue test? Plain and simple, does it stick to your tongue? You will know if it does as it is the strangest feeling.

With a location as the number one clue, things looked positive for my small subjects. I live near the Morrison hogback in Colorado, where evidence of the dinosaurs is prevalent.  Many sea creature fossils can be found on this is the ancient coastline.  Yes, that would be the answer to Question A.  I found them in Morrison, Colorado, which is a paleontologist dream.

The answer to Question B. is also yes. I don't hold a Ph.D. in Geology, nor am I a Paleontologist, far from it, but that doesn't mean I can't do a little detective work. My small fossil bones certainly look like fossil bones. They look the same as the small fossil dinosaur bone I bought in a rock shop in Estes Park. With the help of a magnifying glass, I could see different canals and webbed structures of the bone, sure signs that the object was of biological origin. That with the fact, I found these small chips a few years back on private property where I kept my horses near Morrison were promising. They do look like fossil bones.

Question C., do they pass a tongue test? The porous nature of some fossil bones will cause them to stick to your tongue if you lick them, though you might want to have a glass of water handy if you feel compelled to try this. Yes, mine stuck, but no one told me to be prepared for the craziest sensation.

My small specimens have passed all three questions and are most likely fossil bone and not rock. But what kind of animal did they once belong to is an entirely different question.  I would have to give them up to be destroyed to gather enough DNA to tell, and because I love my rock collection, the chances of that happening are zero.