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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

DOLOMITE


DOLOMITE (Dolomit—Dolomite—ƒоломит) (de Saussure, H.B. 1792), after Dieudonné Silvian Guy Tancréde (Déodat) Grater de Dolomieu (1750-1801), who described its characteristics and occurrences.

Composition & Properties. Carbonate – CaMg[CO3]2, trigonal system. Admixtures: iron, manganese, zinc, cobalt, chromium and others. Hardness 3.5-4. Density 2.8-3.1. Glass luster, pearl one on cleavage planes, dull one in aggregates. Cleavage in three directions. Fragile. Dolomite is found as well-formed crystals of isometric or flattened shape, often with deviated edges, which have a saddle shape. In crystals, dolomite is transparent to translucent, in aggregates it is non-transparent to translucent. Color: colorless, white, gray, green, light blue, brownish, rose. As an ornamental stone, massive kidney-shaped aggregates of dolomite are of interest; they are fine-grained to porcelain-like with conchoidal break. According the admixtures, they classify the following varieties: magnocalcite or calcareous dolomite with calcite admixture; ferrous dolomite, or ankerite brownish because of he admixture of iron. Rose dolomite with the admixture of manganese more than 23% they call mangandolomite, or greinerite. Rose dolomite with the admixture of cobalt up to 3% it is used to call cobalt dolomite; and green one colored with Cr2O3chrome-dolomite. Black dolomite has its color because of inclusions of hard bitumen.

Ornamental rocks. Some colored and patterned varieties of carbonate rocks are used as ornamental stones: algal dolomite, dolomite marble, serpentine dolomite and dolomite breccia. Marl (mergel) is a massive fine-grained or slate clay-carbonate rock of the sedimentary origin. Beside clay minerals, it consists dolomite and calcite, and also here can be gypsum and anhydrite. Its color is mainly light or pale. Some massive varieties are of interest as ornamental stones. Among them, we should mention ornamental shelly marl and light bluish or yellowish-gray flame marl, or color marlstone, greenish because of admixture of glauconite. Among metasomatic rocks of quartz-carbonate content, they use bright colored varieties of list-wanites as ornamental stones.

Deposits. Well-formed, large, transparent crystals of dolomite are found in hydrothermal veins. Dolomite-containing rocks are formed in chemical genesis sedimentary layers and in the process of metasomatism. In Russia, dolomite marbles are known in South Karelia. Even in the 18th cent., they exploited there the Belaya Gora deposit with high-quality ornamental Tivdiya marble. Besides, there are deposits of stromatolite dolomites there. Among metasomatic-transformed rocks in Karelia, there is serpentine dolomite and variegated in color, stripped krivozerite from the region of Kondopoga at Onezhskoye Lake locality. It contains admixtures of quartz, orthoclase and hornblende. In the South Urals, ornamental bioorganic limestone or reef limestone with fossilized remains of ancient sea-weeds has received the name lemesit. At the Satka deposit in the Chelyabinsk Region, they find ornamental varieties of dolomite. In the Middle Urals, near Yekaterinburg, they exploit the Berezovskiy and Nevyanskoye deposits of listwanites. This metasomatic rock, formed at the contact of serpentinite with ultra-basic rocks, is composed with dolomite and breunerite with admixture of chrome mica – fuchsite, talc and pyrite. Texture and structure of listwanites vary. Its color is green, red, gray and more rarely yellow. Ornamental listwanites are found in the Northern Caucasus, in the Krasnodar Region, for instance, the Tkhachskoye deposit; and also in the Kuznetskiy Alatau. In 1991, in Yakutia, in the Olekminskiy Dist., they discovered a deposit of dolomite breccia – radunit. This pale rose to red-brown ornamental rock is mainly of dolomite content. A variety of texture is typical for it: wavy-stripped, fluidal, spotty, breccia. In the Amur Region, there is the Depskoye deposit of ornamental green listwanite. It is situated on the right bank of the Zeya River, near the mouth of the Dap River, at the contact with a massifs of hyperbasites. They have calculated the resources of quality ornamental stone at this deposit. In Armenia, they exploited two deposits of listwanite – Sarydashskoye and Shorja. Listwanites are known also in Azerbaijan at near Kälbäjär (Kalbäcar), and Kyrgyzstan. In Uzbekistan, there is the Sultan Uiz-Dag of listwanite deposit, and at the Yakhton rare-metal deposit in the Samarqand Region, they discovered ornamental serpentinous dolomite breccia. In Mongolia, there is the Han Oyuut deposit of listwanite.

n Scotland, they exploit a deposit of dark gray dolomite with white spots, so called leopard stone. In Spain similar ornamental black dolomite is called teruelita, after the discovery location near Teruel, Aragon Region. There, they also extract listwanite, which has the local name duello. In the Navarra Region, at the Eugui deposit, transparent crystals of green dolomite up to 20 cm, were found. In Italy, in the region of Tuscany, near Miemo, they found crystals of green dolomite, which received the local name miemite. In Switzerland, in crystals up to 15 cm. in cavities of sugar-like dolomite at Lengenbach, Binntal; and in crystals up to 12 cm. at Lamma, near Fiesh, both Valais Canton. In the Graubunden Canton, near Tarasp, occurred crystals of green dolomite – taraspit, their color is connected with the admixture of nickel. This light green dolomite with a pattern of chromium-containing clay minerals is the main component of the ornamental rock, which has the same name. In Austria, at the Striben deposit, Styria, crystals of dolomite in alpine veins reached 19 cm. in their length. In Austria and Italy, dolomite breccia – ruin marl colored with hematite admixture is extracted as an ornamental stone. In Yugoslavia, at the Trepça deposit, Kosovo Dist., they found crystals of dolomite up to 25 cm. in cross-section. In Czech Rep., red dolomite with cobalt-admixture and as variety of mangandolomite – kutnahorite at the Pribram deposit was discovered. In Romania, at the Ocna de Fier deposit, they found rare dolomite pseudomorphs after magnetite up to 3 cm. in size. From Algeria, from the Djelfa deposit, crystals of collection-quality dolomite are sent to the market.

In the U.S.A., findings of large colored crystals of dolomite are known in ore veins of the states of Oklahoma, Kansas, Missouri and Iowa, and also in dolomite marls of the Lockport deposit, New York State. As an ornamental stone, rose dolomite – sugar stone from Michigan is very popular, as well as multicolored dolomite from Minnesota and Vermont. In Canada, large transparent crystals of dolomite were found at the Saint Estashe deposit, Québec Prov., and in the North-West Territories, in the Baffin Land from crystals of light rose dolomite they made faceted stones up to 23 ct. In Brazil, transparent crystals of dolomite up to 18 cm occur at the Brumado deposit, Bahia.

Synonyms. Magnesio-calcite | Smoky calcite | Greinerite, after the Greiner deposit, in Southern Tyrol, Italy | Siliceous lime stone | Listwanite (listvenit), after its “leaf” color, Russ. name | Nevyansk green marble, or Nevzansk listwanite, after the discovery location near Nevyansk, Middle Urals, Russia | Marl, from Lat. “marga” – lime clay | Miascite, obs. | Muricalcite | Perlspath | Picrite, from Gk. “picros” – bitter | Rautenspath, Germ. | Rudolffite |~ spar: bitter ~, brown ~, dolomite ~, orthorhombic ~, pearly ~, calcite-talc ~.

Treatment. Transparent, colorless, pale yellow or pale blue crystals of dolomite spar are of interest as collection material, according these purposes sometimes they are faceted. In the U.S.A., from colorless dolomite, from gypsum concretions of the New Mexico State they made faceted stones up to 15 ct., and in Spain, from dolomite from the Eugui deposit, they made faceted stones up 100 ct. Colored varieties of dolomite ornamental rocks are good material for stone-carving, sometimes they are cut in cabochons. During archaeological excavations at sites of 2-1 centuries B.C. they found beads from marl. In the State Hermitage, SPb., there is a vase from Nevyansk listwanite, 70 cm. high. A similar vase is exhibited in the Ural Geological Museum, Yekaterinburg.

Similarity. Minerals similar to dolomite are carbonates – calcite and magnesite.

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