Aragonite
Current inventory:  2 gems
 

  
Aragonite is named after the location of its discovery, Molina de Aragón, Spain.

Discovered in 1797;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

CaCO₃

Calcium Carbonate

Molecular Weight:

100.09 gm

Composition:

Calcium

40.04 %

Ca

56.03 %

CaO

Carbon

12.00 %

C

43.97 %

CO₂

Oxygen

47.96 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Carbonates

Strunz 8th Ed. ID:

5/B.04-10

Nickel-Strunz 10th Ed. ID:

5.AB.15

5 : CARBONATES (NITRATES)
A : Carbonates without additional anions, without H₂O
B : Alkali-earth (and other M²⁺) carbonates

Related to:

Aragonite Group. Trimorphous with Calcite and Vaterite.

Members of Group:

Aragonite Group: Aragonite, Cerussite, Strontianite, Witherite

Varieties:

Flos Ferri, Plumboan Aragonite, Strontian Aragonite, Zincian Aragonite

Synonyms:

Arragonite, Arragon Spar, Chimborazite, Conchite, Ctypeite, Iglite, Igloite, Ktypéite, Oserskite, Pisa Carolina, Stillatitius lapis, Winnieite

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Isolated crystals short to long prismatic, also acicular with chisellike terminations, dipyramidal, thick tabular, to 30 cm; as columnar crystal aggregates and crusts, globular, reniform, pisolitic, coralloidal, stalactitic, internally fibrous or banded.

Twinning:

Common by repeated contact twinning, yielding pseudohexagonal columnar trillings; also polysynthetic lamellae and striations.

Physical Properties

Cleavage:

Distinct on {010}, Imperfect on {110} and {011}

Fracture:

Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

3.5 - 4.0

Density:

2.95 (g/cm³)

Luminescence:

Fluorescent; pale rose, yellow, white or bluish, with greenish or white phosphorescence under LWUV; yellowish under SW UV. Cathodoluminescent.

Radioactivity:

Not Radioactive pale rose, yellow, white or bluish, with greenish or white phosphorescence under LWUV; yellowish under SW UV.

Optical Properties

Color:

Colorless, White, also Gray, pale shades of Yellow, Blue, Violet, Green, Red; Colorless in transmitted light.

Transparency:

Transparent to Translucent

Luster:

Vitreous, Resinous on fracture surfaces

Refractive Index:

1.530 - 1.685  Biaxial ( - )

Birefringence:

0.155

Dispersion:

Weak; r < v

Pleochroism:

None

Occurances

Geological Setting:

Converts to calcite over geologic time. A primary precipitate in warm marine waters, as oolites and carbonate mud, a principal detrital sedimentary component as the hard parts of many marine micro-organisms, shells and skeletons; also from evaporite deposits; in sinter at hot springs and dripstone in caves; characteristic of high-pressure, low-temperature (blueschist facies) metamorphism; as amygdules in basalt and andesite; a secondary component in altered ultramafic rocks.

Common Associations:

Gypsum, Sulfur, Celestine (evaporite deposits); Pumpellyite, Lawsonite, Glaucophane, Quartz (blueschist); Calcite, Dolomite, Hydromagnesite, Brucite, Magnesite (altered ultramafics).

Common Impurities:

Sr, Pb, Zn

Type Locality:

Molina de Aragón, Guadalajara, Castile-La Mancha, Spain

Year Discovered:

1797

View mineral photos:

Aragonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Aragonite is a rare member of the Aragonite group of minerals that also includes Cerussite and Witherite. Aragonite is a beautiful but little seen gem and is truly a rare collector's gem. It is too soft for jewelry wear and faceted gems are usually very small. Aragonite is the second most common polymorph of natural calcium carbonate, the first being Calcite. A polymorph means that it has the same chemical formula as Calcite but a different crystal structure. Aragonite is usually formed in limestone caverns, hot springs and the oxidized zone of ore deposits.

The best current sources of gem quality Aragonite crystals are Bilin, Ústí Region, Bohemia, Czech Republic; Tazouta, Morocco; and Tsumeb, Namibia.
 

  
Aragonite gems for sale: