Calcite is a carbonate mineral with a formula CaCO3 that is found worldwide in sedimentary, metamorphic and igenous rocks. It crystallizes in a trigonal crystal system and forms well-shaped crystals adopting over 800 described crystal forms (the most common being rhombohedrons and scalenohedrons). The variety of the mineral Iceland spar is transparent and it is used for its double refraction used in optics. The color of the mineral is caused by impurities (Co(II) ions in cobaltoan calcite). The mineral has two other polymorphs that can be found in nature – aragonite (tetragonal) and vaterite (hexagonal). The polymorphs are metastable at normal conditions and converts to calcite [Xyla]. The vaterite is the phase that crystallizes spontaneously first from aqueous media and it rapidly turns into calcite. It is however stabilized by the presence of organophosphorous compounds (e.g. living organism). It is used in biomedicine due to its biodegrability and unique physical properities [trushina]. Aragonite is stabilized by the ions such as Mg2+. The three polymorphs can be distinguished in numerous ways. The easiest way is the use of infrared spectroscopy. The calcite shows characteristic bands at 714 cm-1, 876 cm-1, 1800 cm-1 and the broad band at about 1400 cm-1 [Xyla].
At the locality Maglovec quarry, Vyšná Šebastová, Prešov Co., Slovakia rhombohedral crystals of calcite covered by a thin layer of iron oxides are found in cavities. The unknown samples collected were identified by a chemical and instrumental analysis. The vigorous reaction with hydrochloric acid giving off carbon dioxide and the infrared spectrum measured helped to identify the mineral as calcite besides the mineral similiar in appearance – chabazite.
Calcite, Maglovec quarry, Vyšná Šebastová, Prešov Co., Slovakia
Aragonite, Podrečany, Slovakia