Kaltsiidi

Kaltsiidi, known in English as calcite, is a common carbonate mineral with the chemical formula CaCO3. It is a major constituent of limestone and marble and occurs widely in sedimentary, metamorphic, and hydrothermal environments. Calcite forms in a variety of habits, most commonly rhombohedral crystals, as well as scalenohedra and tabular forms. It crystallizes in the trigonal (rhombohedral) crystal system and exhibits perfect rhombohedral cleavage in three directions.

Calcite has a Mohs hardness of 3 and a specific gravity around 2.71. Pure calcite is colorless and transparent, but impurities can give it a wide range of colors, including white, gray, pink, orange, green, or brown. It is readily dissolved by acids and effervesces vigorously in cold or warm hydrochloric acid. It is also highly birefringent, splitting light into two rays; common refractive indices are about n_o ≈ 1.486 and n_e ≈ 1.658.

Geologically, calcite forms through biological and chemical precipitation in carbonate-rich waters, in limestone and dolostone, and as a primary mineral in marble; it also occurs in hydrothermal veins and metamorphic rocks. It is a major industrial mineral: it provides the bulk of lime and cement materials and is used as a building stone (marble) and in the chemical industry. In optics, transparent calcite varieties (Iceland spar) are valued for their strong double refraction and were historically used in polarizing devices.

Notable varieties include Iceland spar, which is highly transparent, and dogtooth spar, a common scalenohedral form. The term calcite derives from the Latin calx, calcis, meaning lime.