DOLOMITE: Spain (4.5)
Dolomite is a rarely seen gem with distinctive Birefringence (as a carbonate) but is too soft and fragile for wear Spanish crystals are widely sold to collectors so transparent material is fairly abundant.
Dolomite Value
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Dolomite Information
| Data | Value |
| Name | Dolomite |
| Crystallography | Hexagonal (R). Crystals rhomb shaped, sometimes with curved faces; saddle-shaped; massive or granular; twinning common. |
| Colors | Colorless, white, gray, green, pale brown, pink (Mn present). Ankerite is tan to brown, and kutnahorite is pink. Dolomite may also be pink due to Co. |
| Luster | Vitreous to pearly. |
| Hardness | 3.5-4: varies with direction in crystal. |
| Density | 2.85, as high as 2.93; ankerite, 2.93-3.10. |
| Birefringence | 0.179-0.185. (Ankerite, 0.182-0.202). |
| Cleavage | Perfect I direction. Fracture subconchoidal. Brittle. |
| Stone Sizes | Massive material is generally carved; often it is stained pretty colors and may be naturally color banded. Faceted dolomite from New Mexico reaches a size of about 5 carats. Spanish material can provide stones over 100 carats. Private Collection: 18.38 (Spain). |
| Luminescence | Orange, blue, pale green, creamy white, weak brown in SW. Orange, blue, pale green, creamy white in LW. |
| Spectral | Not diagnostic. |
| Formula | CaMg(CO3)2 + Fe, Mn, Zu, Pb, Co. Note: CaFe(CO3)2 = Ankerite. CaMn(CO3)2= Kutnahorite. There is a complete series from dolomite, through ferroan dolomite, to ankerite. |
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 (-).
Indices increase from dolomite values with increasing substitution of iron.
Occurrence: In sedimentary rocks; in Mg-rich igneous rocks that have been altered; geodes.
Quebec, Cananda; Mexico; Brazil; Germany; Austria; Switzerland.
Missouri, Oklahoma, Kansas: so-called Tri-State Mineral Region.
Keokuk, Iowa: in geodes.
New Mexico: transparent material, cuttable.
Lingua, Navarra, Spain: magnificent crystals and clusters, often large size, perfectly formed and completely transparent.
Pribram, Czechoslovakia: cobaltian dolomite (pink).
Czechoslovakia and Hungary: kutnahorite.
Ankerite is a mineral of veins and hydrothermal or lowtemperature deposits.
Comments: Dolomite is a rarely seen gem with distinctive Birefringence (as a carbonate) but is too soft and fragile for wear Spanish crystals are widely sold to collectors so transparent material is fairly abundant.
Name: After Deodat Dolomieu, French engineer and mineralogist.
