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Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO 3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed ...
The origin of the carbonate-rich septaria is still debated. One possibility is that dehydration hardens the outer shell of the concretion while causing the interior matrix to shrink until it cracks. [ 36 ] [ 34 ] Shrinkage of a still-wet matrix may also take place through syneresis , in which the particles of colloidal material in the interior ...
Calcite rafts are thin accumulations of calcite that appear on the surface of cave pools; Hells Bells, a particular speleothem found in the El Zapote cenote of Yucatan in the form of submerged, bell-like shapes; Lava tubes contain speleothems composed of sulfates, mirabilite or opal. When the lava cools, precipitation occurs.
Construction marble is a stone which is composed of calcite, dolomite or serpentine that is capable of taking a polish. [20] More generally in construction , specifically the dimension stone trade, the term marble is used for any crystalline calcitic rock (and some non-calcitic rocks) useful as building stone.
Limestone often contains larger crystals of calcite, ranging in size from 0.02 to 0.1 mm (0.79 to 3.94 mils), that are described as sparry calcite or sparite. Sparite is distinguished from micrite by a grain size of over 20 μm (0.79 mils) and because sparite stands out under a hand lens or in thin section as white or transparent crystals.
Image showing the six most common speleothems The "Witch’s Finger" in the Carlsbad Caverns, New Mexico. A stalagmite (UK: / ˈ s t æ l ə ɡ ˌ m aɪ t /, US: / s t ə ˈ l æ ɡ m aɪ t /; from Greek σταλαγμίτης (stalagmítēs); from Ancient Greek σταλαγμίας (stalagmías) 'dropping, trickling' and -ίτης (-ítēs) 'one connected to, a member of') [1] is a type of ...
Scientists have argued for a biological origin of stromatolites due to the presence of organic globule clusters within the thin layers of the stromatolites, of aragonite nanocrystals (both features of current stromatolites), [18] and of other microstructures in older stromatolites that parallel those in younger stromatolites that show strong ...
Chalk is a soft, white, porous, sedimentary carbonate rock.It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor.