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.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|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.|
|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.|
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.