Aragonite
CaCO3 [CNMNC approved formula]
Named for the type locality, Molina de Aragón, Spain.
| IMA status : | Valid species (Pre-IMA 1790) Grandfathered |
| CLASSIFICATION | |
| Dana (8th edition) : |
14.01.03.01 |
| (14) Anhydrous Carbonates | |
| (14.01) with Simple Formula A+ CO3 | |
| (14.01.03) Aragonite Group (Orthorhombic: Pmcn) | |
| Nickel-Strunz (10th edition) : |
05.AB.15 |
| (05) Carbonates and Nitrates | |
| (05.A) Carbonates without additional anions, without H2O | |
| (05.AB) Alkali-earth (and other M2+) carbonates | |
| Crystal system: | Orthorhombic System |
| Point group (H-M): | mmm (or 2/m 2/m 2/m) — dipyramidal |
| Unit cell: | a = 4.959 Å, b = 7.968 Å, c = 5.741 Å |
| Crystal Habit: | Crystals acicular or chisel-shaped, elongated, thick tabular or pyramidal; frequently twinned as sixlings; columnar; fibrous |
| Twinning: | Common on {110}, contact or penetration as pseudo-hexagonal aggregates |
| Color: | Colorless, white, yellowish, grey, blue, green, lavender |
| Diaphaneity: | Transparent to translucent |
| Luster: | Vitreous to resinous |
| Hardness (Mohs): | 3.5 to 4 |
| Measured Density: | 2.95 g/cm3 |
| Cleavage: | 3; {010} distinct, {110} and {011} indistinct |
| Tenacity: | Brittle |
| Streak: | White |
| Polymorphism and Series: | Trimorphous with calcite and vaterite |
| Geologic 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. |
| Mineral Association: | Gypsum, sulfur, celestine (evaporite deposits); pumpellyite, lawsonite, glaucophane, quartz (blueschist); calcite, dolomite, hydromagnesite, brucite, magnesite (altered ultramafics) |
| Synonyms/varieties: | Flos-Ferri (branch-like var.), mossottite, tarnowitzite (Pb-rich var.), Nicolsonite (Zn-rich var.) |
| Luminescent Properties: | Cathodoluminescent, fluorescent red or yellow under LW and SW UV, phosphorescent. |
| Other Properties: | Gemstone Rare. BioMineral. |
Twinned crystalOrigin: Molina de Aragon, Spain (type locality)
Sample size: 2 x 1.5 cm (top)
Photo: Tom Loomis
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Photo: Tom Loomis
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Photo: Tom Loomis
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Photo and Owner: Lou Perloff
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Photo and Owner: Lou Perloff