Aragonite

ARAGONITE (has been found for the first time among the depositions of gypsum within the Aragon region of Spain * EN: aragonite, aragon spar; DE: Aragonit; FR: aragonite; ES: aragonita; RU: арагонит) is the mineral of the class of carbonates, Ca[CO3].

Aragonite is the metastable modification of the calcium carbonate, which is stable at the normal pressure thanks to the impurities. Unlike the calcite, it more often contains impurities of SrO (up to 3.9% within the zeyringite) and PbO (up to 7.5% within the tarnovicite); there are also observed the impurities of Mg, Ba. It crystallizes into the rhombic crystal systems. The structure is sub-laminated. There is at its foundation the deformed most dense hexagonal packing of the Ca2+ cations. The radicals of [CO3]2- are situated between the cationic layers. It may be commonly found in the form of crusts, flowstones, fibrous, coral-shaped ("iron flowers"), oolitic ("pea stone"), and fine-grained banded (marble onyx) aggregates; there are less common the elongated crystals, trillings, and twins. It is colourless or snow-white, often colorated into the gray, blue, yellow, purple, and other colours. The hardness is 3.5-4. The density is approximately 3000 kilograms per cubic metre. It is the supergenous, hydrothermal, and biogenic mineral. The variety of aragonite, namely, the conchite, is one of the main constituent parts of the nacreous layer of the shells of many mollusks and pearls.

It is characteristic the location of aragonite within the biogenic deposits of sulfur. It is also identified within the lagoon and marine sediments, within evaporites, within the cave formations, within the certain crusts of weathering, and oxidation zones of the sulfidic deposits. It is deposited from the thermal water spring sources and geysers, it may be found within the amygdules of basalts together with zeolites, and so on. It gradually transitions into the calcite. The largest deposits of the high quality aragonite, with the reserves of several billion tonnes, have been explored on the coastal shelf near the Bahamas islands. The development of the underwater tabular deposit of aragonite is conducted within the shallow waters near the Lake Bimini with the floating dredgers. The extracted pulp is thickened and beneficiated at the hydrocyclone separators and vibrating sizing screens. It is the raw material for the chemical, cement, and glass industries. Beautifully coloured, translucent varieties of aragonite (marble onyx) are the (decorative) semi-precious stones.