Saturday, February 09, 2019

Geological State Symbols Across America - Colorado

The next state up for the Geological State Symbols Across America is:


You can find any of the other states geological symbols on my website here: (being updated as I go along this year).

                                                                                        Year Established
State Rock: Yule Marble                                                          2004
State Mineral:  Rhodochrosite                                                 2002
State Gemstone: Aquamarine                                                  1971
State Fossil: Stegosaurus                                                          1982

I also have two Geology of the National Parks Through Pictures that I have done for Colorado previously. These include:

Black Canyon of the Gunnison National Park
Dinosaur National Monument
Hovenweep National Monument
Mesa Verde National Park
Rocky Mountain National Park
Yucca House National Monument

State Rock: Yule Marble
Be it enacted by the General Assembly of the State of Colorado: 

SECTION 1. Part 9 of article 80 of title 24, Colorado Revised Statutes, is amended BY THE ADDITION OF A NEW SECTION to read: 

24-80-912.7. State rock. Yule Marble is hereby made and declared to be the state rock of the state of Colorado.

The Colorado Yule Marble Quarry. Image courtesy of the Colorado Geological Survey.

Marble is a metamorphosed variety of the sedimentary rock limestone. This means that the original sedimentary rock underwent periods of increased temperatures and pressures to change the rock itself. The primary minerals in marble are calcite (CaCO3) or dolomite ((Ca,Mg)CO3) but it will usually have other mineral contaminates mixed in as well (i.e., clay, mica, quartz, pyrite, and iron oxide, etc.). Since, the primary mineral in marble is calcite, most marbles will have a white color with swirls of darker colors (the contaminates) but marbles can be found in many different colors depending on what impurities were present in the initial limestone. During metamorphism of the original limestone, the calcite is recrystallized to form interlocking crystals, which will usually destroy any remnants of the original rock, including any fossils present.

Tomb of the Unknown Soldier. Photo by Thomas Loker Photography (

The unique feature of the Yule Marble, found near the town of Marble, Colorado, is that the marble is one of the purest marbles ever quarried (meaning it lacks most of those impurities). For this reason it was chosen as the decorative stone on the Lincoln Memorial in Washington DC. The Yule Marble started out as the dark-blue Mississippian age Leadville Limestone. During the Tertiary, parts of the Leadville Limestone underwent contact metamorphism along the edges in contact with the uplifted granitic Treasure Mountain dome. After recrystallization, the Leadville Limestone was metamorphosed into the distinctive white marble known today. Along with the Lincoln Memorial, Yule Marble has been used for the Tomb of the Unknown Soldier, which was the largest single piece of marble ever quarried at the time. They also supplied some of the national cemetery headstones. However due to problems financing and running the mine, not many other notable uses have been made of the Yule Marble.

State Mineral: Rhodochrosite 
Be it enacted by the General Assembly of the State of Colorado: 

SECTION 1. Part 9 of article 80 of title 24, Colorado Revised Statutes, is amended BY THE ADDITION OF A NEW SECTION to read: 

24-80-912.5. State mineral. Rhodochrosite is hereby made and declared to be the state mineral of the state of Colorado.
Samples of rhodochrosite cabochons from Argentina. Image courtesy of

Rhodochrosite is a manganese carbonate mineral (chemical formula (Mn, Fe, Mg, Ca)CO3) with a light pink to bright red color. As you can see with the chemical formula the manganese is frequently replaced with other elements like iron, magnesium, and/or calcium. These substitutions present problems with providing definitive mineral properties since the substitutions cause the specific gravity, hardness, and color of the mineral to vary. Generally though, rhodochrosite has a hardness of 3.5-4 with 3 directions of perfect, rhombohedral cleavage. Rhodochrosite is often found in association with silver mines and is sometimes mined as a by-product in those mines. Rhodochrosite can also be found filling the veins and fractures within metamorphic rocks. In this instance, the minerals are often built up over time with separate mineralization events, each one possibly producing different shades of pink within the mineral. Rhodochrosite can be used as a manganese ore, however there is often not enough of it when found to make it economically viable. Since rhodochrosite is so soft, its use in even jewelry is limited, where it usually ends up being used just as a natural mineralogical sample.

Rhodochrosite crystals with tertahedrite from the Sweet Home Mine, Alma, Colorado. Image courtesy of the Colorado Geological Survey

Rhodochrosite, is extremely rare in well-formed crystals. That is the reason that the Sweet Home Mine, near Alma, Colorado is so unique (such as the sample to the right). This is one of the few mines in the world to produce specimen quality rhodochrosite samples. Formerly a silver mine that opened in 1873, the mine was leased to a rhodochrosite company who started excavating high grade rhodochrosite samples. They mine by blasting holes in the rock that are 2mx2mx2m, and continue the process forming tunnels. Once a potential rhodochrosite pocket is located, special tools are brought to carefully extract the specimens, where they are then taken to be cleaned and prepared for sale. The usually pink color, as seen in the image to the upper left, is not the only variety seen in Colorado samples. Colorado rhodochrosite also comes in a translucent red crystal variety that is recognized worldwide for its beauty (as seen in the image to the right). Beyond just the Sweet Home Mine, rhodochrosite can be found in 18 counties within Colorado, with the largest rhodochrosite crystal ever found, the 6.5 inch Alma King, being found within the Sweet Home Mine itself.

State Gemstone: Aquamarine
Chapter 325
An Act concerning state emblems, and providing for the designations of a state gemstone.
Be it enacted by the General Assembly of the State of Colorado:

Section 1. Article 8 of chapter 131, Colorado Revised Statutes 1963, as amended, is amended BY THE ADDITION OF A NEW SECTION to read:

131-8-12. State gemstone. The aquamarine is hereby made and declared to be the state gemstone of the state of Colorado.

L. 71: p. 1221, § 1. C.R.S. 1963: § 131-8-12.
An aquamarine crystal from the Shiga Valley of northern Pakistan. Image courtesy of Arkenstone,, and

Aquamarine is a greenish blue variety of beryl (Be3Al2Si6O18), named for the seawater in which it looks like. It has a hardness of 7.5-8 and often forms perfect, six-sided prismatic crystals. Although it can be found in duller colors; when heated to very high temperatures the mineral attains its characteristic sky-blue color. Even though beryl, and therefore aquamarine, has a very high hardness, its uses seem to be generally limited to jewelry and display items. Crystals of aquamarine are relatively common, however they still demand a high price, due to this intrinsic beauty of the specimens. Display quality aquamarine crystals can be found in Brazil, Pakistan, China, Russia, Myanmar, as well as several localities within the United States, among other localities worldwide. Quality aquamarine specimens within the US can be found in Colorado, California, Idaho, Connecticut, and Massachusetts.

The location of the Tertiary Princeton batholith near Mt. Antero and White Mt. where the aquamarines in Colorado have been mined. Map courtesy of Switzer. 1939.

Prospecting for aquamarine began in the late 1800's in the Mt. Antero area of Colorado. Many aquamarine crystals have been found in vugs (holes) within granite pegmatites of the Tertiary Princeton batholith. There are several different types of pegmatites within this region, with two different beryl pegmatites, only one of which contains vugs, or pockets. It is this pegmatite that is the most economically viable for aquamarine specimens. These vuggy beryl pegmatites include not only aquamarine crystals but also crystals of other minerals like microcline, smoky quartz, albite, and fluorite. The veins and pegmatites where the aquamarine has been found are mostly contained within an area roughly 3 miles across; an area that contains the summits of Mt. Antero and White Mt. (as seen in the map to the left). These pegmatites formed at temperatures that ranged from 200°C up to 600°C. Other areas within Colorado that also contain quality aquamarine specimens include Mt. Baldwin and Mt. Princeton, which are both located nearby to White Mt. and Mt. Antero.

State Fossil: Stegosaurus
Executive Order D0002 82

WHEREAS, Colorado enjoys a long and colorful history which extends well into the prehistoric era in which numerous dinosaurs and other now-extinct flora and fauna flourished; and

WHEREAS, the Stegosaurus lived in Colorado 150 million years ago in the Mesozoic era during the Jurassic period; and

WHEREAS, there are only six skeletons of the Stegosaurus on public display in the United States, including one on public display at the Museum of Natural History in Denver, Colorado, which was found and dug up by a teacher and students at Canon City High School; and

WHEREAS, the Stegosaurus, like all dinosaurs, makes a continuing contribution to modern living through fossil fuels which are comprised of the remains of dinosaurs and other once-living matter from prehistoric times; and

WHEREAS, the Stegosaurus has stimulated the interest of numerous Colorado school children to participate in the political process through their efforts to have the Stegosaurus established as a state fossil by the Colorado General Assembly; and

WHEREAS, three other states have established state fossils; and

WHEREAS, the establishment of a state fossil for the State of Colorado would be a benefit to the tourism industry of the state and would provide a positive conclusion to the important effort of numerous school children in Colorado to participate in our political process;

NOW, THEREFORE, I, Richard D. Lamm, Governor of the State of Colorado, pursuant to the authority vested in me under the laws and constitution of the State of Colorado, DO HEREBY declare that the Stegosaurus shall be considered the State Fossil for the State of Colorado and shall remain as the State Fossil pursuant to this Executive Order until such time as the General Assembly takes action to establish a State Fossil by statute.

GIVEN under my hand and the Executive Seal of the State of Colorado, this 28th day of April, A.D., 1982.
Stegosaurus at the Field Museum, Chicago, IL. Photo by Jim Lehane.

Stegosaurus was one of the earliest dinosaur finds during the infamous Cope and Marsh Bone Wars (find out more about that here). The first Stegosaurus fossils were discovered in 1876 in the Morrison Formation of Colorado by M.P. Felch and were named by Marsh in 1877. The original fossils were discovered north of the town of Morrison, CO. The name Stegosaurus means roof lizard, a name that goes back to when Marsh first described the animal thinking that the plates laid flat along its back, creating a roof. It wasn't until Marsh discovered another example of Stegosaurus with the plates still in situ (in place) that he realized his mistake. About 80 specimens of Stegosaurus have since been discovered in the Morrison formation, stretching from Colorado to Wyoming.

was an herbivore, that lived about 150 million years ago during the Jurassic period. The animal is most well known for the twin row of bony plates that lined its back and a set of spikes on its tail. Scientists are not certain of the use of the plates and several theories have been postulated including defense, display, or even heating/cooling pads (blood vessels ran through the plates allowing the air/sun to heat or cool the plates as needed); however it is pretty universally accepted that the spikes at the end of the tail were for defensive purposes. One of the most commonly known "facts" about Stegosaurus was that it had a very small brain for the size of the animal (it is about the size of a bus, 30 ft in length, with a brain the size of a hot dog). Because of the comparably small size of the brain, scientists at one time thought that Stegosaurus must have had a second "brain", or nerve ball cluster, that operated as a second brain somewhere along the spinal column. This idea came from the discovery of an enlarged canal along the pelvic region, however this theory has since been rejected by scientists. Stegosaurus had a toothless beak, with rounded peg-like teeth further back in its mouth, and a weak jaw, so it likely ate low lying plants like ferns and cycads.


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