Teacher’s Corner

Much of the CGS website is under heavy re-construction and will be for some time. The Publications area is working normally, but there is a lot of content from our original site that was in desperate need of updating. Please bear with us as we gather new information and rewrite hundreds of pages of material, gather and properly caption high-resolution images and otherwise bring you some very cool new and archival material never before seen! Stay in touch by subscribing to the >RockTalk< blog where we will announce new items periodically.

The CGS has free resources for teachers to help educate students about Colorado’s diverse and fascinating geology. Drop us an email and we will be happy to point you to a variety of resources including posters, bookmarks, maps, and field guides.

Available as free PDF downloads our RockTalk newsletters covers a broad range of geologic phenomena in Colorado. Topics range from diamond mines to snow avalanches to mining subsidence and more.

We’ve also decided to revive RockTalk as the RockTalk blog so that we can continue to bring you interesting, informative, and timely postings related to our mission.


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.