Quantcast
Gemstones 250x250

The Mineral dolomite

Dolomite Pearl Spar

Dolomite is a very common mineral, and is known for its saddle-shaped curved crystal aggregates. A unique, isolated Dolomite occurrence in Eugui, Spain has provided colorless transparent crystals that resemble the Iceland Spar variety of Calcite. The occurrence of Kolwezi, in the Congo, has produced some fascinating, cobalt-rich specimens that are a beautiful hot pink color and highly popular.

Dolomite forms in a different crystal class, differing from the Calcite group minerals. This can be noted by the fact that Dolomite generally forms more elongated crystals than those of the Calcite group. In addition, Dolomite never occurs in scalenohedral crystals, whereas minerals of the Calcite group do.

Dolomite is used to describe both a mineral and a rock. The mineral is the pure form with a defined crystal structure and chemical formula, whereas dolomite rock is composed chiefly of the mineral Dolomite, but also contains impurities such as Calcite, Quartz, and feldspar.

Chemical Formula

CaMg(CO3)2

Color

Colorless, white, gray, peach, pink, yellow, and orange. Rarely yellow, green, red, and black.

Crystal System

Hexagonal

Properties

Streak
White
Hardness
3.5 - 4
Transparency
Transparent to translucent
Specific Gravity
2.8 - 3.0
Luster
Vitreous, pearly
Cleavage
1,3 - rhombohedral
Fracture
Conchoidal
Tenacity
Brittle
Other ID Marks
Occasionally fluorescent bluish-white or pink in shortwave ultraviolet light.

Crystal Habits

Common in groups of small rhombohedral crystals, often with curved, saddle-like faces. Also prismatic, (although usually slightly curved), grainy, botryoidal, coxcomb, and massive. Uncommon in large rhombohedrons or rhombohedral aggregates.

3D Crystal Atlas

Additional Information

Composition
Calcium magnesium carbonate. The amount of calcium and magnesium in most specimens is equal, but occasionally one element may have a slightly greater presence than the other. Small amounts of iron and manganese are sometimes also present.
In Group
Carbonates;
Striking Features
Curved crystals and crystal groupings, associate minerals and environment
Environment
In sedimentary rock such as dolomite rock and limestones. Occasionally in high-temperature metamorphic rocks and low-temperature hydrothermal veins.
Rock Type
Igneous, Sedimentary, Metamorphic

Varieties

 -   Hot-pink, cobalt-rich variety of Dolomite.
 -   Rock composed mostly of the mineral Dolomite, but also contains impurities such as Calcite, Quartz, and Feldspar.
 -   Grouping of white to pinkish curved Dolomite crystals with a pearly luster.

Uses

Dolomite is used to make magnesia, which has important medicinal applications. It is important in the chemical industry for the preparation of magnesium salts. It is also used in soil mixtures to lower the acid levels of the soil.

Dolomite specimens from the the Midwest localities in the Tri-State region of Oklahoma, Missouri, and Kansas are popular collector items. The clear transparent specimens from Spain and the hot-pink variety from the Congo make rare and unusual specimens that are highly sought after by collectors. Dolomite rock is used as an ornamental and structural stone, and for extracting certain metals from their ores. 

Noteworthy Localities

Many localities have produced fine Dolomite specimens. As it is a very common mineral, only several select ones are listed here.

The most prominent European Dolomite occurrence is Eugui, Navarra, Spain, where water-clear, transparent crystals uniuque to this occurrence were found in fairly large crystal sizes. Other European localities include the Traversella, Piedmont, Italy; Binn Tal, Wallis, Switzerland; Oberdorf an der Laming, Styria, Austria; the Castilla quarry, Setiles, Spain; and Kapnik, Maramures Co., Romania.

Two important African deposits, famous among collectors for the hot-pink cobalt-rich Dolomite, are Kolwezi, Katanga (Shaba), Congo (Zaire); and Bou Azzer, Morocco. Tsumeb, Namibia, was an outstanding producer of specimen-grade Dolomite, especially of the green, copper-rich type. Other rich worldwide deposits are the Shangbao mine, Hunan Province, China; Brumado, Bahia, Brazil; and Santa Eulalia, Chihuahua, Mexico.

The best U.S. occurrences of Dolomite are in the tri-state mining district of Missouri, Kansas, and Oklahoma, especially the localities of Picher and Joplin, Ottawa Co., Oklahoma, where curved groups of lustrous pink, peach, and white crystals occurred with Galena, Sphalerite, and Chalcopyrite. Two other good Midwest localities are Black Rock, Lawrence Co., Arkansas; and the Sweetwater Mine, Reynolds Co., Missouri. Dolomite was also found in Pennsylvania in the Binkley-Ober Quarry, Manheim, Lancaster Co. 

A large dolomite body extends southwest of Lake Ontario in Ontario, Canada, and crosses into the New York border at the Niagara Falls area. It runs several hundred miles through central New York. Several dolomite and limestone quarries in this area have produced nice Dolomite crystals. These include the following New York quarries: the LaFarge Quarry, Lockport, Niagara Co., New York; the Penfield Quarry, Penfield, Monroe Co.; the Walworth Quarry, Walworth, Wayne Co.; and the Herkimer Diamond mining localities. In Canada, this dolomite zone has produced nice crystals at the Canal Dump in Niagara Falls, Ontario. Mont Saint-Hilaire, Quebec, has produced Dolomite in the form of unusual green crystal clusters.

Distingushing Similar Minerals

Calcite - Lower hardness, easily effervesces in cold, dilute hydrochloric acid, lacks rounded crystals.
Aragonite - Lacks the cleavage of Dolomite, crystals not curved.
Quartz - Much harder.
Gypsum - Much softer, is sectile and slightly flexible.
Anhydrite - Different cleavage, does not effervesce.
Magnesite - Massive and fine-grained specimens cannot be distinguished from Dolomite by ordinary methods.


Close

Copyright © 2019. Minerals.net

View on Full Site