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Calcite seas existed in Earth's history when the primary inorganic precipitate of calcium carbonate in marine waters was low-magnesium calcite (lmc), as opposed to the aragonite and high-magnesium calcite (hmc) precipitated today. Calcite seas alternated with aragonite seas over the Phanerozoic, being most prominent in the Ordovician and ...
The alternation of calcite and aragonite seas through geologic time A calcite sea is a sea in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. An aragonite sea is the alternate seawater chemistry in which aragonite and high-magnesium calcite are the primary inorganic carbonate precipitates.
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 ...
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.
A complex diagenetic history can be established by optical mineralogy, using a petrographic microscope. Carbonate rocks predominantly consist of carbonate minerals such as calcite, aragonite or dolomite. Both the cement and the clasts (including fossils and ooids) of a carbonate sedimentary rock usually consist of carbonate minerals. The ...
Draperies or curtains are thin, wavy sheets of calcite hanging downward Bacon is a drapery with variously colored bands within the sheet; Rimstone dams, or gours, occur at stream ripples and form barriers that may contain water; Cave crystals. Dogtooth spar are large calcite crystals often found near seasonal pools
This calcite shell provides protection for the crustaceans, meaning between molting cycles the crustacean must avoid predators while it waits for its calcite shell to form and harden. Various types of foraminifera observed through a microscope using differential interference contrast.
These fragments mostly take the form of calcite plates ranging from 0.5 to 4 microns in size, though about 10% to 25% of a typical chalk is composed of fragments that are 10 to 100 microns in size. The larger fragments include intact plankton skeletons and skeletal fragments of larger organisms, such as molluscs , echinoderms , or bryozoans .