Rhodochrosite is a manganese carbonate, MnCO3. It is not considered a gemstone, even though fine examples of the large, red, rhombic crystals have a value of several thousand dollars. Gems are valued for their use in jewelry; because rhodochrosite has a much lower hardness than most gemstones, its use in jewelry is very limited. The rhodochrosite crystals from Colorado are valued solely for their own natural intrinsic beauty. Rhodochrosite’s crystal habit is the rhombohedron typical of carbonate minerals. It is also found in Colorado as massive, dogtooth, disc-like, radiating, granular, stalactitic, and rosette forms. Although it is most commonly pink and opaque, Colorado’s translucent red variety is prized the world over, commonly bringing prices in the tens of thousands of dollars. Rhodochrosite is found in eighteen of Colorado’s counties associated with gold, silver, lead, zinc, and molybdenum ores. Earth’s largest rhodochrosite crystal, the Alma King, is on display at the Denver Museum of Nature and Science. This 6.5-inch crystal was collected in 1992 from the Sweet Home Mine, high in the Mosquito Range west of the old mining town of Alma in Park County.
The Sweet Home Mine was claimed in 1872 and issued US Patent #106, one of the earliest patents granted under the General Mining Law of 1872. It was worked as a silver mine in the late 1800’s and then off and on again into the 1950’s. Rhodochrosite used to be discarded as waste on Sweet Home’s dumps but the large, deep red colored, perfectly formed rhombohedral specimens, which no other location produces, has now brought Sweet Home more fame as a rhodochrosite mine than it ever had as a silver mine.
Rhodochrosite (red) on tetrahedrite [(Cu,Fe,Zn,Ag)12Sb4S13] (black) and quartz [SiO2] (white) from Sweet Home Mine, specimen provided by Dave Bunk. Photo credit: Jeff Scovil.
How Did Rhodochrosite Become The State Mineral?
Governor Owens signed a bill on April 17, 2002 sponsored by Senator Ken Chlouber and Representative Carl Miller making rhodochrosite the state mineral. Colorado becomes the 20th state to have an official state mineral. Others include minerals such as gold (Alaska, California), coal (Kentucky), and galena (Missouri and Wisconsin).
John Ghist’s Earth Science class at Platte Canyon High School near Bailey, Colorado was studying rocks and minerals when they became aware that Colorado did not have a State Mineral. After some debate, the students decided that rhodochrosite, because of its red color (similar to ‘Colorado’ for ‘reddish’ in Spanish) should be the state mineral. They wrote a letter to State Representative Carl Miller suggesting that rhodochrosite be designated the official State Mineral. Representative Miller introduced the legislation and thanks to John Ghist and his students, within three months rhodochrosite was designated the Colorado State Mineral.
At the urging of a Girl Scout Troop, Representative Betty Boyd introduced a bill to make Yule Marble Colorado’s official State Rock. As legislators considered the proposal, they were never very far from the real thing, because some of the floors and trim in the State Capitol Building are made of Yule Marble. It has also been used in the construction of more than 30 buildings in Colorado and more than 100 buildings across the country including the Lincoln Memorial and the Tomb of the Unknowns.
Cogent points about Yule Marble:
· The stairs and floors of the State Capitol Building were supposed to be made of Yule Marble.
· The stone was used in the construction of more than 30 buildings in Colorado and more than 100 additional buildings across the country including the Lincoln Memorial and the Tomb of the Unknowns.
· It is possible to quarry larger blocks of Yule Marble than most other marbles in the world.
· The character of the stone is exceptional and is better for sculpting than Michelangelo’s favorite Carrara Marble.
· Its chemical purity, as well as its small and uniform grain size has led to its use in many experiments in rock mechanics.
The story of how Yule marble became Colorado’s State Mineral
Fact Sheet on Yule Marble from Girl Scout Troop 357:
Colorado is the Centennial State. Colorado has a red Official State Mineral, rhodochrosite. Colorado has a blue Official State Gemstone, aquamarine. If the state rock were white, the Official Geological symbols would be red, white, and blue. The Yule Marble is white. The Yule Marble has been used in many famous buildings and sculptures.
· The Lincoln Memorial in Washington DC.
· In the Washington Monument, each state contributed a 20″ x 40″ rock to line the inside of the monument, and Colorado chose the Yule Marble.
· The Tomb of the Unknowns, currently being renovated, is made of the largest single block of marble produced in the United States.
· Colorado State Capitol building.
· Cheesman Memorial, Denver.
· Colorado State Museum, Denver.
· Denver Court House.
As the state known for the majestic Rocky Mountains, it seems odd that the state does not yet have an official state rock. Only nine states have three geological symbols (rock, gem and mineral), and none of them have the color combination of red, white, and blue. Only four states have a state rock that matches the rock in the Washington Monument for that state. The Yule Marble is a strong, beautiful rock. It is composed of 99.5% pure calcite. The grain size yields brilliant cleavage sparkles in the unpolished stone. It has lasted almost 100 years in the humid environment of DC. The first major use of the Yule Marble was in the Colorado State Capitol building, in 1895.
The Stegosaurus lived in the area we now know as Colorado one hundred and fifty million years ago during the Mesozoic era. It is believed that a typical Stegosaurus weighed ten tons though its brain weighed only two and one-half ounces. There are only six skeletons of the Stegosaurus on public display in the United States, one of which may be viewed at the Denver Museum of Nature and Science. This skeleton was discovered by a teacher and students from Canon City High School.
The Stegosaurus was designated as the official state fossil on April 28, 1982 by executive order of Governor Richard D. Lamm.
The mountain peaks of Mount Antero and Mount White in Chaffee County, Colorado are among the finest localities known for gem quality aquamarine. They are also among the highest in elevation — at 13,000 to 14,200 feet. The granite rock of these peaks contains pegmatite bodies that are characterized by large miarolitic cavities containing the gem quality aquamarine crystals. The cavities are found through a vertical area of a mere 500 feet. The crystals in these cavities range in color from light blue to pale blue and deep aquamarine green, and in size from very small to 6 cm in length.
The aquamarine was adopted as the official state gemstone on April 30, 1971, by an act of the General Assembly. Citation: House Bill 1104, 1971; Colorado Revised Statute 24-80-912.