Rhodochrosite: Argentina, cross section of stalactite, with cabochons (15 x 20 mm). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Rhodochrosite belongs to two solid solution series. It’s the manganese (Mn) analogue in a series with iron (Fe) dominant siderite. It holds the Mn-end of a series with calcium (Ca) dominant calcite, too.
Massive material from Argentina occurs in large pieces. Gem cutters have cabbed and carved this material into decorative as well as useful objects, such as boxes. Aggregate rhodochrosites can show white or grey jagged bands. Facetable, translucent pink material cuts stones up to about 20 carats.
The Capillitas mine in Argentina’s Catamarca Province has also produced very rare trapiche-like rhodochrosites. Some sections of stalactitic rhodochrosites have revealed stunning, star-like “floral” patterns.
South African rhodochrosites have a rich, rose red color but rarely occur in facetable crystals. The largest cut gems are in the 60-carat range.
Colorado produces pink gems, perhaps the loveliest of all. Faceters have cut flawless gems up to about 15 carats. However, most stones range under five carats in size.
Rhodochrosite: Peru, (71.5), South Africa (9.42), Argentina (3.95). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Calcium in rhodochrosite’s formula reduces its refractive index (RI) and specific gravity. Iron and zinc, in contrast, increase them. This also affects its birefringence. High birefringence causes a pronounced doubling effect in rhodochrosites.
Single crystals may be zoned, causing the RI to vary up to 0.01 within a space of one inch in some material.
Rhodochrosites will effervesce in warm acids. (Please keep in mind that acid testing is a destructive test. It can endanger both the gem and the tester. Never conduct this test on a finished gem. Use this procedure as a last resort for gem identification only).
“Rhodochrosite,” Corner Pocket area, Watercourse Raise, Sweet Home Mine, Alma, Colorado, USA, 2.3 x 1.8 x 1.5 cm. © Rob Lavinsky, www.iRocks.com. Used with permission.
Since rhodochrosite serves as an important manganese ore, scientists have synthesized this material for research purposes. Synthetic material has also appeared in jewelry, particularly as beads and cabs.
Gem buyers may also encounter simulants or imitations of rhodochrosites, such as dyed calcite beads and talc-calcite aggregates. These pieces can be distinguished relatively easily through gemological testing.
Rhodonites and rhodochrosites may be misidentified due to their color and appearance. Furthermore, both are popular materials for decorative and practical carvings. Opaque rose red rhodonites can also show banding, though it appears darker and dendritic. Like rhodochrosites, rare transparent rhodonites may also be faceted. However, rhodonites have greater hardness and different optical properties.
Opaque rhodochrosites may receive wax or plastic impregnation to improve durability and color. Hot point testing may reveal this.
The state of Colorado produces spectacular crystals, pink to deep red, small to three inches on an edge. The world’s finest rhodochrosite comes from Alma, Colorado. Some is facetable, red material. Other localities also produce pink faceting rough.
“Rhodochrosite,” Sweet Home Mine, Alma, Park County, Colorado, marquise cut, 7.0 x 9.0 x 8.0 mm, 8.61 cts. © Rob Lavinsky, www.iRocks.com. Used with permission.
San Luis, Catamarca Province, Argentina produces massive and banded material, including stalactites up to four feet long! These have concentric structures that display interesting bull’s-eyes when cross-sectioned. Some Argentinian material is translucent and facetable.
Other notable sources include:
- Butte, Montana: crystal groups (non-gem).
- Magdalena, Mexico: sometimes in cuttable pieces.
- Peru: facetable, pink crystals.
- Hotazel, South Africa: facetable, deep reddish crystals.
- Canada; China; Japan; Kazakhstan.
- Smithsonian Institution (Washington, DC): 20.8, 15.2, and 9.5 carats (South Africa).
- Devonian Group (Calgary, Alberta, Canada): 5.95 (red, South Africa).
- National Museums of Canada (Ottawa, Ontario): 18.05 (red oval, South Africa).
- Private Collection: 59.65 (red oval, South Africa).
With perfect cleavage, low hardness, and heat sensitivity, rhodochrosites make challenging stones to cut and wear. Nevertheless, in protective settings, these gems can serve as beautiful stones for a variety of jewelry uses.
Avoid cleaning any rhodochrosites with mechanical systems and any cleaning solutions with acids. Instead, use a soft brush, mild detergent, and warm water only.
Be aware that the temperatures a jeweler’s torch reaches can damage plastic or wax impregnated gems. Therefore, if you don’t know if your loose rhodochrosites are treated, have them tested by a gemological lab before setting.
Store your rhodochrosites separately from other stones to avoid contact scratches.