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Minerals - Aragonite

Minerals - Aragonite

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Datum izida:3/23/2007 7:09:00 AM
Oblikovanje:Matjaž Učakar
Motiv:Aragonite
Tisk:Poštovní tiskárna cenin, Praha
Izvedba:4-colour offset
Papir:Tullis rusell
Velikost:
Zobčanje:Comb
Ilustracija:
Fotografija:Miran Udovč
Pošta:
Poštna številka:

Minerals - Aragonite

<b>ARAGONITE</b><p>Slovenian karst caverns are known in the world also by their decorative formations. Water rich with carbon dioxide dissolves karstified rocks, and the minerals in the form of a calcareous sinter crust are formed in all kinds of shapes. Most of them form the mineral calcite, while aragonite is rare. Slovenian most important natural monument with aragonite crystals, presented on the stamp, is the Ravenska Cave at Cerkno. Up to 10 cm long crystal needles form beam-like bunches on the cavern ceiling and walls.Aragonite was named by the mineralogist Werner after the Spanish region Aragón in 1796. According to its chemical structure this is calcium carbonate, CaCO3. The orthorhombic crystal lattice determines the columnar and needle-like shapes. Parallel growing crystals combine into irregular branching stalactitic forms. Bent sintery and crystal branching bunches are called helictites.More aragonite is formed at higher cavern temperatures. In Slovenia it is formed in rare caverns only due to the special chemical structure of the water there. When it contains more magnesium, it stops the calcite’s growth and in its place aragonite is formed.Aragonite is also formed from the water of some warm springs that is cooling down. Changing accretions of aragonite and organic materials produce pearls in some shells. Aragonite forms most of the molluscs’ shells and corals’ skeletons. <p> Dr. Uroš Herlec