Rice Northwest Museum Rhodochrosite Exhibit


Rhodochrosite is a manganese carbonate (MnCO3). The carbonates are a group of minerals that contain the anion group CO32-, and are subdivided into the calcite, aragonite, dolomite or hydrated carbonate subgroups. Rhodochrosite belongs to the calcite subgroup. These carbonates are known for having rhombohedral symmetry, which results in the formation of rare rhombohedron shaped crystals.

The name rhodochrosite is derived from the Greek for rose-colored. Rhodochrosite is most commonly pink or red, but may sometimes occur as yellow, grey or brown crystals. Pink and red colors occur when the rhodochrosite has a high manganese content, but some substitution of iron in place of manganese causes other colors. Its density also depends on the amount of manganese present, with a lower density associated with low iron content. Rhodochrosite is white when powdered (white streak), and has a vitreous luster. It has similar hardness to other carbonates, with a Moh’s value between 3.5 and 4. It is found most commonly in hydrothermal veins, and is associated with other carbonates, sulfide minerals, fluorite, barite and quartz.

Good crystals of rhodochrosite are valued by mineral collectors, and rare, red, rhombohedron crystals are prized most highly. The Sweet Home Mine in Alma, Colorado, produced a number of exceptional rhodochrosite crystals in the 1990s. The most famous of these were the Alma King and the Alma Rose. Richard and Helen Rice bought both the Alma King and Alma Rose at the Tucson Gem and Mineral Show in 1993. They sold the Alma King to the Coors Brewing Company, who subsequently facilitated the Denver Museum of Nature and Science to acquire and display the specimen. The Rices kept the Alma Rose, and you can see it in the Main Gallery at the museum today. The Alma Rose is one of the museum’s signature specimens. It consists of five large (~9 cm) rhodochrosite rhombohedron crystals on a matrix of quartz, calcite, sphalerite and tetrahedrite.

Make sure you see the Alma Rose and watch the movie about the Sweet Home Mine next time you visit the museum! And don’t forget to find some of our other rhodochrosite specimens too!