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Class: Carbonates (Nitrates)
Group: Aragonite

In evaporite deposits; in sinter at hot springs; characteristic of high-pressure, low-temperature metamorphism; a secondary component in altered ultramafic rocks (Anthony et al., 2001—2005). Faceted specimens are very rare. The largest faceted stone is a 110 carat from Bílina, Czech Republic (Arem, 1987: 46).
Aragonite — specimen 0190
Aragonite — specimen 0190, photo © NMNHS

Original description: ‘Arragonite’ Hauy, O., 1791. Sur l’Arragonite de Werner — Bulletin des Sciences, par la Société Philomathique de Paris 2: 67—68 [view in ‘Library’].

Type locality: Gallo river, Molina de Aragón, Guadalajara, Castile-La Mancha, Spain.

Type material: unknown.

Etymology: named for the type locality, the village of Molina de Aragón, Spain.

Distribution: many localities, but fine crystals are uncommon: Czech Republic: Bohemia, Ústecký kraj, Bílina; Italy: Sicily, Agrigento; Morocco: Oriental Region, Oujda; Namibia: Tsumeb; Spain: Castile-La Mancha, Guadalajara, Molina de Aragón (Anthony et al., 2001—2005).



Essential elements: carbon (C), oxygen (O), calcium (Ca).

Crystal data

Crystallography: orthorhombic — dipyramidal. Crystal habit: isolated crystals short to long prismatic along [010], also acicular with chisellike terminations, dipyramidal, thick tabular with forms {001}, {110} and {010}, to 30 cm; as columnar crystal aggregates and crusts, globular, reniform, pisolitic, coralloidal, internally fibrous or banded. Twinning: common by repeated contact twinning on {110}, yielding pseudohexagonal columnar trillings (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {010}, distinct; on {110} and {011}, imperfect (Anthony et al., 2001—2005). Fracture: subconchoidal (Arem, 1987: 46). Tenacity: brittle (Arem, 1987: 46). Hardness: 3.5—4 (Arem, 1987: 46). Density: 2.93—2.96 g/cm3 (Lazzarelli, 2012). Luminescence: fluoresce red or yellow under UV, phosphorescent, cathodoluminescent (Anthony et al., 2001—2005).

Optical properties

Colour: colourless, white, also grey, pale shades of yellow, blue, violet, green, red; colourless in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous, resinous on fracture surfaces (Anthony et al., 2001—2005). Refractive index: 1.525—1.686 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Birefringence: 0.155. Dispersion: weak (Anthony et al., 2001—2005). Pleochroism: none (Arem, 1987: 46).

Material from ‘Repository’

1 specimen: 0190 — 2.16 ct, Czech Republic, Bohemia, Ústecký kraj, Bílina.

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