Dolomite, 16.94 cts, “Trillion Brilliant” cut, Eugui, Esteribar, Navarre, Spain. © Rob Lavinsky, www.iRocks.com. Used with permission.
Although transparent dolomite crystals are fairly abundant and popular collector’s items, faceted gems are soft, fragile, and rarely seen in jewelry. However, massive material can be carved into decorative pieces.
| Data | Value |
|---|---|
| Name | Dolomite |
| Crystallography | Hexagonal (R) (trigonal). Crystals rhomb shaped, sometimes with curved faces; saddle-shaped; massive or granular; twinning common. |
| Refractive Index | 1.500-1.750 |
| Colors | Colorless, white, gray, black, blue, green, pale brown, pink (Mn present). Ankerite is tan to brown, and kutnohorite is pink. Dolomite may also be pink due to Co. |
| Luster | Vitreous to pearly |
| Hardness | 3.5-4, varies with direction in crystal. |
| Fracture | Subconchoidal |
| Specific Gravity | 2.85, as high as 2.93; ankerite, 2.93-3.10. |
| Birefringence | 0.179-0.185. (Ankerite, 0.182-0.202). |
| Cleavage | Perfect 1 direction |
| Luminescence | Orange, blue, pale green, creamy white, weak brown in SW. Orange, blue, pale green, creamy white in LW. See "Identifying Characteristics" below. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long, UV-Short |
| Enhancements | Dyeing |
| Typical Treatments | Dyeing |
| Transparency | Transparent to opaque |
| Absorption Spectrum | Not diagnostic |
| Formula | CaMg(CO3)2 + Fe, Mn, Zu, Pb, Co. Ankerite: CaFe(CO3)2 . Kutnohorite: CaMn(CO3)2. |
| Optics | Dolomite: o = 1.679-1.703; e = 1.500-1.520. Uniaxial (-). Ankerite: o = 1.690-1.750; e = 1.510-1.548. Uniaxial (-). See "Optical Properties" below. |
| Optic Sign | Uniaxial - |
| Etymology | Dolomite is named after Deodat Dolomieu, French engineer and mineralogist. Ankerite is named after Mathias Anker, Austrian mineralogist. Kutnohorite (also known as kutnahorite) is named after the type locality, Kutna Hora, Czech Republic. |
| Occurrence | Dolomite: in sedimentary rocks; in Mg-rich igneous rocks that have been altered; geodes. Ankerite is a mineral of veins and hydrothermal or low-temperature deposits. |
Dolomites: New Mexico (gem about 2 cts, rough 2 inches across). Photo © Joel E. Arem, PhD, FGA. Used with permission.
A carbonate mineral, dolomite forms a series with both the very rare ankerite, in which iron (Fe) exceeds magnesium (Mg), and the manganese (Mn)-dominant kutnohorite. Dolomites that contain Fe (but not in excess of Mg) are known as ferroan dolomites. Manganoan dolomites contain Mn, of course, which gives these stones a pink color.
Transparent dolomite crystals are difficult for faceters to cut. Dolomites have a low and variable hardness of 3.5 to 4, which varies along its four crystal axes, as well as perfect cleavage. These factors also make it a fragile stone for jewelry use. They are more liable to scratch and break than most jewelry stones.
Any dolomite ring stones should have protective settings. Earrings, pendants, and brooches would make more practical options for these gems. However, you’re more likely to find dolomites in mineral collections than jewelry collections. Faceted dolomites would appeal most to collectors of unusual gems or aficionados of the art of gem cutting.
Dolomite: New Mexico (3.06). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Dolostones are rocks made from a mix of minerals, though their main carbonate is dolomite or ankerite. You may find some of these rocks referred to as dolomites. However, gemologists should distinguish between dolostones and dolomites.
Objects made from dolostone lapidary material have much greater wearability than dolomites. Artists have carved large sculptures as well as small decorative objects from dolostones.
Sculpted dolostone heads, from the Monument to the War of Independence by Jaan Koort, 1924. Rapla, Estonia. Photo by Stemugram. Licensed under CC By-SA 3.0 EE.
A variety of dolostone, caymanite was first discovered in the Cayman Islands. This material can contain color bands of red, orange, white, black, and brown. With a hardness of 6 to 7 on the Mohs scale, this polycrystalline dolostone has greater toughness than crystalline dolomite. Caymanite has become a popular lapidary stone.
Caymanite necklaces on display on top of raw caymanite stone. Photo by S.S. Licensed under CC By-SA 3.0.
This dolostone from the Kona Hills in Michigan contains stromatolites, fossilized algae. This lapidary material can show mottling, markings, or bands of multiple colors, such as black, brown, cream, gray, orange, pink, red, or yellow.
A fist-size carved ball of Kona dolomite. Photo by Jarek Tuszynski. Licensed under CC By 4.0.
As carbonates, dolomites have distinctive birefringence. Faceted pieces may show doubling of facet images.
As Fe substitution increases, the refractive indices of series minerals also increase from the dolomite values.
Although dolomites have a uniaxial optic character, anomalously biaxial specimens may occur.
Faceted dolomite showing the facet doubling effect. New Mexico (2 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Manganoan varieties may fluoresce pale pink through intense red, but weaker in longwave ultraviolet light.
Dolomites may display triboluminescence, which means it luminesces when held or rubbed.
Fluorescent dolomite crystals, on display at the Mineralogical Museum, Bonn, Germany. Photo by Ra’ike. Licensed under CC By-SA 3.0.
Unlike other carbonates, like calcites, dolomites may not effervesce when exposed to weak, room temperature hydrochloric acid (for example, during acid testing). However, the mineral may effervesce if powdered or composed of fine-grained crystals. (Please note, acid testing is a destructive test. Conduct this test only as a last resort on an inconspicuous spot and never on a finished gem).
Calcite and magnesite gems may resemble dolomites. They may show similar colors, transparency, and birefringent doubling effects. Calcites have a lower hardness, but dolomites and magnesites fall within the same hardness range. (Scratch testing is another destructive test of last resort). Magnesite has a higher specific gravity (SG) than dolomite.
Dolomite has many industrial applications, including agricultural, manufacturing, medical, and petrological. This mineral even has properties useful for studying particle physics. Not surprisingly, scientists have synthesized dolomites, including crystals, for many research projects. However, there is no known use of this lab-created material for jewelry purposes. With the natural material so abundant and not well-suited for jewelry, this would be most unlikely.
Sintered dolomite (powdered, then heated and compressed to a solid) has been used as bead material for South Sea pearl cultivation.
Dyed dolomites have surfaced as imitations of more well-known and expensive gem materials, such as lapis lazuli and turquoise. Dyed dolomites may also resemble howlites. In one unusual case, SG and optical tests exposed beads sold as dyed howlite lapis lazuli simulants as, in fact, dyed dolomites.
Dolomites occur in abundance in many locales across the globe. However, the most well-known source of gem-quality material, Eugua, Navarra, Spain, produces magnificent, often large, perfectly formed and transparent crystals and clusters.
The famous Muzo emerald mine in Colombia has yielded very rare light blue dolomites. Most likely, natural radiation caused this unusual coloration.
Sources of pink cobaltoan dolomites include the Democratic Republic of Congo, the Czech Republic, and Morocco.
Cobaltoan dolomites on calcite, 4.3 x 3.3 x 3.0 cm, Kakanda deposit, Katanga Copper Crescent, Katanga (Shaba), Democratic Republic of Congo. © Rob Lavinsky, www.iRocks.com. Used with permission.
Notable gem-quality sources in the United States include the following:
Other notable gem-quality dolomite sources include the following:
The Czech Republic, Hungary, Slovakia, and South Africa produce kutnohorite.
The Cayman Islands and Hungary produce caymanite.
Kutnohorite crystals, 6.2 x 6.1 x 3.8 cm, Wessels Mine, Kalahari Manganese Fields, South Africa. © Rob Lavinsky, www.iRocks.com. Used with permission.
Gem cutters often carve and stain massive material. Sometimes, natural color banding occurs.
Faceted dolomites from New Mexico can reach about 5 carats in size. The Spanish material can provide stones over 100 carats.
Store dolomites and any jewelry made with them in a cloth bag or box, away from other harder gems. This will prevent contact scratches. Clean dolomites only with a soft brush, mild detergent, and warm water. See our gemstone jewelry cleaning guide for more recommendations.
Dolomite: Spain (4.5). Photo © Joel E. Arem, PhD, FGA. Used with permission.
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