May 12 2014
Topics Covered
Introduction to Aragonite
Properties of Aragonite
How to Identify Aragonite
Global Distribution
Occurrence of Aragonite and Useful Mineral Association
References
Introduction to Aragonite
Chemical Formula – CaCO3
Aragonite has been named after the Aragon region in Spain where it was first discovered. This mineral belongs to the Aragonite group. Aragonite is trimorphous, with calcite and vaterite.
Properties of Aragonite
The following are the key properties of aragonite:
- Cell Data
- Space group: Pmcn
- a=4.9611(4)
- b=7.9672(6)
- c=5.7407(4)
- Z=4
- Crystal Data
- Orthorhombic, Pseudohexagonal
- Point group: 2/m 2/m 2/m
- Isolated crystals, short to long prismatic along [010], also acicular with chisel like terminations, dipyramidal thick tabular with forms {001}, {110} and {010}, to 30cm; as columnar crystal aggregates and crusts, globular, reniform, pisolitic, coralloidal, stalactitic, internally fibrous, or banded
- Twinning: Common by repeated contact twinning on {110}, yielding pseudohexagonal comlumnar trillings; also polysynthetic lamellae and striations || [001]
- X-ray powder pattern: 4.39 (100), 2.987 (100), 2.850 (79), 10.50 (44), 6.63 (43), 7.06 (42), 3.624 (41)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| CO2 |
43.95 |
43.97 |
| MgO |
0.03 |
- |
| CaO |
55.96 |
56.03 |
| Insol |
0.13 |
- |
| Total |
100.07 |
100.00 |
- Optical Properties
- Transparent to translucent
- Color: colorless, white, gray, pale shades of yellow, blue, violet, green, red; colorless in transmitted light
- Streak: white
- Luster: vitreous, resinous on fracture surfaces
- Optical Class: Biaxial (+)
- Orientation: X = c, Y = a; Z = b
- Dispersion = r
- α = 1.530
- β = 1.681
- γ = 1.685
- 2V(meas) = 18o
- Estimated Properties
| Electron density |
Bulk density (electron density) = 2.93 g/cm3
note: Specific gravity of aragonite = 2.93 g/cm3 |
| Photoelectric |
PEAragonite = 5.06 barns/electron
U=PEAragonite x ρ electron density= 14.81 barns/cm3 |
| Fermion index |
Fermion index = 0.0020908312
Boson index = 0.99790 |
Radioactivity
|
Aragonite is not radioactive.
|
How to Identify Aragonite
Aragonite appears as a colorless or white mineral, which sometimes exhibits shades of pale yellow, blue, and violet. It exhibits distinct cleavages on certain axes, and is brittle by nature. It shows cathodoluminescence, fluorescence of red or yellow under LW or SW UV phosphorescent.
Global Distribution
Aragonite is distributed widely. However, the fine crystal form of Aragonite is rare to find. Aragonite is found in the localities listed below:
- Spain – from Molina, Gudalajara Province
- Italy – from Racalmuto, Cianciana, Agrigento (in the form of fine crystals), Sicily
- Slovakia – from Dognacska and Spania Dolina
- Poland – from Tarnowitz, Silesia
- Austria – Erzberg, near Eisenerz, Styria and Leogang, Salzburg
- Czech Republic – from Spitzberg, Horenz near Bilina
- England – Cleator Moor, Frizington, Cumbria
- Morocco – fine crystals from Touissit mine, near Oujuda and Tazouta near Sefrou
- Namibia – large crystals from Tsumeb
- USA – from caves at Bisbee, Cochise Co. Arizona. Large crystals from Lake Arthur, Chavez Co. and Guadalupe Co. New Mexico. Passaic Mine, Sterling Hill
Occurrence of Aragonite and Useful Mineral Association
Aragonite converts to calcite over geologic time. It is formed as a primary precipitate in warm marine waters, as oolites and carbonate mud. It is a principal detrital sedimentary component, as hard parts of many marine micro-organisms, shells and skeletons; also from evaporate 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.
It is associated with minerals such as gypsum, sulfur, Celestine, pumpellyite, lawsonite, glaucophane, quartz, calsite, dolomite, hydromagnesite, brucite, and magnesite.
References