Aragonite
Aragonite is named after the Aragon region, Spain, where pseudo-hexagonal twinned crystal forms were first recognized.
Aragonite is a polymorph of
calcite, having the same chemical composition but a different physical structure. When aragonite is heated to 400°C it will convert to calcite.
Aragonite occurs in compact, granular, massive or radially fibrous forms. Crystals are often twinned and form pseudohexagonal prisms. They are usually white or colourless but may have brown, grey, green or violet hues. Transparent crystals of aragonite are found in many places, particularly in Bohemia, Spain and the north of England. Massive material is found in horizontal layers. A layered sedimentary marble-like material is sometimes referred to Mexican Onyx and is used for carvings and ornamental objects.
Aragonite forms the basis for many organic gems, such as
coral,
mother-of-pearl and
pearl.
General Information |
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Chemical Formula | Michael O’Donoghue, Gems, Sixth Edition (2006) More from other references |
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Photos of natural/un-cut material from mindat.org |
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Physical Properties of Aragonite |
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Mohs Hardness | 3.5 to 4Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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Specific Gravity | 2.93 to 2.96Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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Tenacity | BrittleArthur Thomas, Gemstones (2009) |
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Cleavage Quality | DistinctArthur Thomas, Gemstones (2009) |
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Fracture | Sub-ConchoidalArthur Thomas, Gemstones (2009) |
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Heat Sensitivity | ModerateArthur Thomas, Gemstones (2009) |
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Optical Properties of Aragonite |
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Refractive Index | 1.525 to 1.686Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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Optical Character | Biaxial/-Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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Birefringence | 0.155Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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Pleochroism | StrongArthur Thomas, Gemstones (2009) |
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Dispersion | LowArthur Thomas, Gemstones (2009) |
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Colour |
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Colour (General) | White, yellowish, reddish, greenish, bluish, violet. Commonly bandedUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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Transparency | Transparent,Translucent,OpaqueUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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Lustre | VitreousArthur Thomas, Gemstones (2009) |
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Fluorescence & other light emissions |
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Fluorescence (General) | Common orange or creamHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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Fluorescence (Short Wave UV) | Green-white, pink, whiteArthur Thomas, Gemstones (2009) |
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Fluorescence (Long-Wave UV) | Pink, whiteArthur Thomas, Gemstones (2009) |
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Crystallography of Aragonite |
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Crystal System | OrthorhombicHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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Habit | Frequently shows pseudohexagonal habit which is caused by combination and twinningMichael O’Donoghue, Gems, Sixth Edition (2006) More from other references |
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Geological Environment |
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Where found: | Typical deposits occur at hot springs, in cavities in volcanic rocks and in cave formation.Arthur Thomas, Gemstones (2009) |
Further Information |
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Mineral information: | Aragonite information at mindat.org |
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Significant Gem Localities |
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| Canada | |
| Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 385 | | Czech Republic | |
| | | Namibia | |
| | | Peru | |
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