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Spanish Aragonite Trilling

The Mineral aragonite




Aragonite and the more common mineral Calcite are polymorphous to each other. Although Aragonite and Calcite contain the same chemical composition, they differ in crystal structure. Aragonite forms orthorhombic crystals, whereas Calcite forms trigonal crystals. Sometimes the crystals of Aragonite and Calcite are too small to be detected, and it is only possible to distinguish these two minerals by complex scientific optical tests. Since the true identity of microcrystalline forms of Aragonite or Calcite may not be known, they may be mislabeled as the wrong mineral.

Almost all Aragonite crystals are twinned growths of three individual crystals that form pseudohexagonal trillings . Therefore, although Aragonite crystallizes in the orthorhombic system, virtually all its crystals are hexagonal shaped. The trillings can be noted from the basal striations on each of the three individual crystals running in different directions, causing a hexagonal crystal to have three striation directions on each base.

Other minerals frequently pseudomorph Aragonite. Calcite commonly pseudomorphs after Aragonite, and although it contains the same chemical composition and crystal forms as Aragonite, it is really Calcite. There are many Aragonite crystals sold to collectors that are in fact really Calcite pseudomorphs after Aragonite. A rare but popular pseudomorph of Copper after Aragonite comes from Corocoro, Bolivia.

Aragonite frequently contains sand inclusions, which give a specimen a brown color. It forms in many environments, but a particularly interesting one is its formation from deposition of hot, mineral-rich springs. The water releases the calcium it contains upon reaching the air, and forms mounds and thick crusts around the springs. When these deposited mounds and crusts are banded, they are sometimes carved and termed "Onyx Marble", "Suisan Marble", "California Onyx", or "Mexican Onyx".

Aragonite is the main component of many organic substances, such as pearl and coral. The iridescent surface of pearl and mother-of-pearl is a layer of Aragonite secreted by mollusks and related invertebrates.

Some forms of Aragonite, especially the Flos Ferri variety, are very brittle and fragile and may easily break when touched. Such specimens need to be handled with utmost care to preserve them.
Chemical Formula CaCO3
Composition Calcium carbonate, sometimes with some strontium, lead, and zinc.
Variable Formula (Ca,Sr,Pb,Zn)CO3
Color Colorless, white, brown, gray, yellow, red, pink, purple, orange, blue, green
Streak White
Hardness 3.5 - 4
Crystal System Orthorhombic
3D Crystal Atlas
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Crystal Forms
and Aggregates
The most common crystallized form is in pseudohexagonal trillings, which can be in the form of long, slender, prismatic crystals or short stubby ones. Rarely occurs as single, untwinned crystals. Many aggregates exist, such as acicular, radiating, fibrous, columnar, stalactitic, botryoidal, pisolitic, oolitic, tuberose, granular, encrusting, and ball-like protrusions of pseudohexagonal crystals.
Transparency Transparent to opaque
Specific Gravity 2.9 - 3.0
Luster Vitreous, dull
Cleavage 3,1 - prismatic ; indiscernible,2
Fracture Subconchoidal
Tenacity Brittle
Other ID Marks 1) May fluoresce blue, pink, yellow, or cream.
2) Clear specimens exhibit a strong double refraction.
Complex Tests Effervesces in acids, even if cold and diluted.
In Group Carbonates; Aragonite group
Striking Features Poor cleavage, twinning habits, strong effervescence, and low hardness
Environment Sedimentary formations and evaporite deposits, hot spring deposits, hydrothermal ore veins, igneous traprock environments, and metamorphic schists.
Rock Type Igneous, Sedimentary, Metamorphic
Popularity (1-4) 2
Prevalence (1-3) 2
Demand (1-3) 2

Aragonite ON EBAY

VARIETIES
 -  Massive, fine grained variety of Gypsum. Occasionally may also refer to a translucent, banded type of Aragonite in the form of Travertine or Tufa.
 -  Filiform variety of Aragonite composed of wormlike intergrowths resembling branching coral.
 -  Strontium rich variety of Aragonite, or mixture of Aragonite and Strontianite. (Ca,Sr)CO3. Also known as Strontian Aragonite.
 -  Zinc rich variety of Aragonite. (Ca,Zn)CO3. Also known as Zincian Aragonite.
 -  Travertine or Tufa in the mineral form of Aragonite or Calcite that exhibits color banding.
 -  Fibrous variety of Gypsum. May occasionally also describe a fibrous form of Calcite or Aragonite.
 -  Lead rich variety of Aragonite, or mixture of Aragonite and Cerussite. (Ca,Pb)CO3. Also known as Plumboan Aragonite.
 -  Mounds of calcium carbonate formed from hot springs that contain calcium-rich water that bubbles up to the earth and cools down, and its capability to hold calcium is reduced. The water eliminates the calcium, and the calcium forms a growing mound of calcium carbonate, which is porous. Travertine is usually Aragonite, although it may also be Calcite.
 -  Aragonite (or Calcite) formed from precipitating water that traps in organic matter, such as leaves, twigs, and moss. Also calcareous mounds formed from deposition of hot springs that trap in organic matter.
POLYMORPHS
Calcite, Vaterite

USES
Aragonite does not have many practical uses, but interesting specimens are popularly collected by mineral collectors. The "Onyx Marble" formed from mineral springs is cut into cabochon and ornaments.

NOTEWORTHY LOCALITIES
The name Aragonite is derived from the location of Molina de Aragon, Spain, where excellent trillings occur at the Gallo river. Spain has produced some of the finest trillings in locations such as Los Molinillos (Minglanilla), the Retamal ravine, and the Salt Mine in Cuenca. Excellent Aragonite also comes from the Agrigento Province in Sicily, Italy, in the famous Sulfur mines. It occurs in Austria in a Siderite mine in Eisenerz, Styria (mainly in the Flos Ferri variety), and in the salt mines of Salzburg. Classic Aragonite has come from the old iron mines at Frizington, Cumbria, England; and from Vitosov, Moravia, Czech Republic.
 
Much specimen material has recently come from Liupanshui, Guizhou Province, China; and one of the largest producers of specimen crystals in all forms of twinned aggregates of reddish-brown crystals is the Tazouta Mine near Sefrou, Morocco.
 
New Mexico has provided many fine specimens in Kelly and Magdalena, Soccoro Co.; at Lake Arthur, near Roswell, Chaves Co; and at Las Cruces, Dona Ana Co. Fine Aragonite has also come from Bisbee, Cochise Co., Arizona; the Grand Deposit Mine, White Pine Co., Nevada; and the Northern Lights Mine, Hussman Spring, Mineral Co., Nevada. Other Western U.S. occurrences are Morro Bay, San Luis Obispo Co., California; the Oquirrh Mountains, Tooele Co., Utah; and Fort Collins, Larimer Co., Colorado. Midwestern and Eastern occurrences are Cave-in-Rock, Hardin Co., Illinois; Berks Co., Pennsylvania; Sterling Hill, Ogdensburg, Sussex Co., New Jersey; and Paterson and Prospect Park, Passaic Co., New Jersey.

COMMON MINERAL ASSOCIATIONS
Quartz, Calcite, Gypsum, Albite, Azurite, Chalcopyrite, Bornite

DISTINGUISHING SIMILAR MINERALS
Calcite - Distinguished by perfect rhombohedral cleavage and by the fact that it is slightly softer. In addition, many Aragonite aggregate types don't exist in Calcite.
Cerussite, Witherite, and Strontianite - Heavier.
Hemimorphite - Harder (4½ - 5), heavier.


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