The Madera Group is a group of geologic formations in northern New Mexico . Its fossil assemblage dates the formation to the middle to late Pennsylvanian period .
105-705: The group consists primarily of marine limestones , and it is exposed in the Sandia Mountains , the Lucero Uplift ( 34°37′16″N 107°17′56″W / 34.621°N 107.299°W / 34.621; -107.299 ), the western Jemez Mountains , the Sangre de Cristo Mountains , and in the Manzano Mountains . The lower section of the group tends to be a gray limestone and the upper an arkosic limestone, and these have been divided into
210-455: A Mohs hardness of 2 to 4, dense limestone can have a crushing strength of up to 180 MPa . For comparison, concrete typically has a crushing strength of about 40 MPa. Although limestones show little variability in mineral composition, they show great diversity in texture. However, most limestone consists of sand-sized grains in a carbonate mud matrix. Because limestones are often of biological origin and are usually composed of sediment that
315-463: A bloom of cyanobacteria or microalgae . However, stable isotope ratios in modern carbonate mud appear to be inconsistent with either of these mechanisms, and abrasion of carbonate grains in high-energy environments has been put forward as a third possibility. Formation of limestone has likely been dominated by biological processes throughout the Phanerozoic , the last 540 million years of
420-423: A desiccator alongside ammonium carbonate [NH 4 ] 2 CO 3 . In the desiccator, ammonium carbonate is exposed to air and decomposes into ammonia , carbon dioxide, and water . The carbon dioxide then diffuses into the aqueous solution of calcium chloride, reacts with the calcium ions and the water, and forms calcium carbonate. The thermodynamically stable form of CaCO 3 under normal conditions
525-519: A food additive it is designated E170 , and it has an INS number of 170. Used as an acidity regulator , anticaking agent , stabilizer or color it is approved for usage in the EU, US and Australia and New Zealand . It is "added by law to all UK milled bread flour except wholemeal". It is used in some soy milk and almond milk products as a source of dietary calcium; at least one study suggests that calcium carbonate might be as bioavailable as
630-452: A phosphate binder for the treatment of hyperphosphatemia (primarily in patients with chronic kidney failure ). It is used in the pharmaceutical industry as an inert filler for tablets and other pharmaceuticals . Calcium carbonate is used in the production of calcium oxide as well as toothpaste and has seen a resurgence as a food preservative and color retainer, when used in or with products such as organic apples. Calcium carbonate
735-434: A carbonate rock outcrop can be estimated in the field by etching the surface with dilute hydrochloric acid. This etches away the calcite and aragonite, leaving behind any silica or dolomite grains. The latter can be identified by their rhombohedral shape. Crystals of calcite, quartz , dolomite or barite may line small cavities ( vugs ) in the rock. Vugs are a form of secondary porosity, formed in existing limestone by
840-616: A central quartz grain or carbonate mineral fragment. These likely form by direct precipitation of calcium carbonate onto the ooid. Pisoliths are similar to ooids, but they are larger than 2 mm in diameter and tend to be more irregular in shape. Limestone composed mostly of ooids is called an oolite or sometimes an oolitic limestone . Ooids form in high-energy environments, such as the Bahama platform, and oolites typically show crossbedding and other features associated with deposition in strong currents. Oncoliths resemble ooids but show
945-449: A change in environment that increases the solubility of calcite. Dense, massive limestone is sometimes described as "marble". For example, the famous Portoro "marble" of Italy is actually a dense black limestone. True marble is produced by recrystallization of limestone during regional metamorphism that accompanies the mountain building process ( orogeny ). It is distinguished from dense limestone by its coarse crystalline texture and
1050-949: A composition reflecting the organisms that produced them and the environment in which they were produced. Low-magnesium calcite skeletal grains are typical of articulate brachiopods , planktonic (free-floating) foraminifera, and coccoliths . High-magnesium calcite skeletal grains are typical of benthic (bottom-dwelling) foraminifera, echinoderms , and coralline algae . Aragonite skeletal grains are typical of molluscs , calcareous green algae , stromatoporoids , corals , and tube worms . The skeletal grains also reflect specific geological periods and environments. For example, coral grains are more common in high-energy environments (characterized by strong currents and turbulence) while bryozoan grains are more common in low-energy environments (characterized by quiet water). Ooids (sometimes called ooliths) are sand-sized grains (less than 2mm in diameter) consisting of one or more layers of calcite or aragonite around
1155-412: A considerable fraction of the limestone bed. At depths greater than 1 km (0.62 miles), burial cementation completes the lithification process. Burial cementation does not produce stylolites. When overlying beds are eroded, bringing limestone closer to the surface, the final stage of diagenesis takes place. This produces secondary porosity as some of the cement is dissolved by rainwater infiltrating
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#17328015398601260-483: A drop of dilute hydrochloric acid is dropped on it. Dolomite is also soft but reacts only feebly with dilute hydrochloric acid, and it usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Impurities (such as clay , sand, organic remains, iron oxide , and other materials) will cause limestones to exhibit different colors, especially with weathered surfaces. The makeup of
1365-637: A few million years, as this is the most stable form of calcium carbonate. Ancient carbonate formations of the Precambrian and Paleozoic contain abundant dolomite, but limestone dominates the carbonate beds of the Mesozoic and Cenozoic . Modern dolomite is quite rare. There is evidence that, while the modern ocean favors precipitation of aragonite, the oceans of the Paleozoic and middle to late Cenozoic favored precipitation of calcite. This may indicate
1470-455: A few thousand years. As rainwater mixes with groundwater, aragonite and high-magnesium calcite are converted to low-calcium calcite. Cementing of thick carbonate deposits by rainwater may commence even before the retreat of the sea, as rainwater can infiltrate over 100 km (60 miles) into sediments beneath the continental shelf. As carbonate sediments are increasingly deeply buried under younger sediments, chemical and mechanical compaction of
1575-410: A filler in paper because they are cheaper than wood fiber . Printing and writing paper can contain 10–20% calcium carbonate. In North America, calcium carbonate has begun to replace kaolin in the production of glossy paper . Europe has been practicing this as alkaline papermaking or acid-free papermaking for some decades. PCC used for paper filling and paper coatings is precipitated and prepared in
1680-435: A limestone sample except in thin section and are less common in ancient limestones, possibly because compaction of carbonate sediments disrupts them. Limeclasts are fragments of existing limestone or partially lithified carbonate sediments. Intraclasts are limeclasts that originate close to where they are deposited in limestone, while extraclasts come from outside the depositional area. Intraclasts include grapestone , which
1785-471: A lower Mg/Ca ratio in the ocean water of those times. This magnesium depletion may be a consequence of more rapid sea floor spreading , which removes magnesium from ocean water. The modern ocean and the ocean of the Mesozoic have been described as "aragonite seas". Most limestone was formed in shallow marine environments, such as continental shelves or platforms . Such environments form only about 5% of
1890-525: A lower diversity of organisms and a greater fraction of silica and clay minerals characteristic of marls . The Green River Formation is an example of a prominent freshwater sedimentary formation containing numerous limestone beds. Freshwater limestone is typically micritic. Fossils of charophyte (stonewort), a form of freshwater green algae, are characteristic of these environments, where the charophytes produce and trap carbonates. Limestones may also form in evaporite depositional environments . Calcite
1995-523: A mechanism for dolomitization, with one 2004 review paper describing it bluntly as "a myth". Ordinary seawater is capable of converting calcite to dolomite, if the seawater is regularly flushed through the rock, as by the ebb and flow of tides (tidal pumping). Once dolomitization begins, it proceeds rapidly, so that there is very little carbonate rock containing mixed calcite and dolomite. Carbonate rock tends to be either almost all calcite/aragonite or almost all dolomite. About 20% to 25% of sedimentary rock
2100-448: A plausible source of mud. Another possibility is direct precipitation from the water. A phenomenon known as whitings occurs in shallow waters, in which white streaks containing dispersed micrite appear on the surface of the water. It is uncertain whether this is freshly precipitated aragonite or simply material stirred up from the bottom, but there is some evidence that whitings are caused by biological precipitation of aragonite as part of
2205-523: A pure quarried source (usually marble ). Alternatively, calcium carbonate is prepared from calcium oxide . Water is added to give calcium hydroxide then carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC) This process is called carbonatation : In a laboratory, calcium carbonate can easily be crystallized from calcium chloride ( CaCl 2 ), by placing an aqueous solution of CaCl 2 in
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#17328015398602310-449: A radial rather than layered internal structure, indicating that they were formed by algae in a normal marine environment. Peloids are structureless grains of microcrystalline carbonate likely produced by a variety of processes. Many are thought to be fecal pellets produced by marine organisms. Others may be produced by endolithic (boring) algae or other microorganisms or through breakdown of mollusc shells. They are difficult to see in
2415-399: A requirement that becomes important at high usage temperatures. Here the percentage is often 20–40%. It also routinely used as a filler in thermosetting resins (sheet and bulk molding compounds) and has also been mixed with ABS , and other ingredients, to form some types of compression molded "clay" poker chips . Precipitated calcium carbonate, made by dropping calcium oxide into water,
2520-532: A resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature. In ceramic glaze applications, calcium carbonate is known as whiting , and is a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze. Ground calcium carbonate is an abrasive (both as scouring powder and as an ingredient of household scouring creams), in particular in its calcite form, which has
2625-478: A source of dietary calcium, but are also a practical industrial source. Dark green vegetables such as broccoli and kale contain dietarily significant amounts of calcium carbonate, but they are not practical as an industrial source. Annelids in the family Lumbricidae , earthworms, possess a regionalization of the digestive track called calciferous glands , Kalkdrüsen, or glandes de Morren, that processes calcium and CO 2 into calcium carbonate, which
2730-870: A variety of shapes and sizes having characteristic narrow particle size distributions and equivalent spherical diameters of 0.4 to 3 micrometers. Calcium carbonate is widely used as an extender in paints , in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble. It is also a popular filler in plastics. Some typical examples include around 15–20% loading of chalk in unplasticized polyvinyl chloride (uPVC) drainpipes , 5–15% loading of stearate -coated chalk or marble in uPVC window profile. PVC cables can use calcium carbonate at loadings of up to 70 phr (parts per hundred parts of resin) to improve mechanical properties (tensile strength and elongation) and electrical properties (volume resistivity). Polypropylene compounds are often filled with calcium carbonate to increase rigidity,
2835-534: Is hexagonal β- CaCO 3 (the mineral calcite ). Other forms can be prepared, the denser (2.83 g/cm ) orthorhombic λ- CaCO 3 (the mineral aragonite ) and hexagonal μ- CaCO 3 , occurring as the mineral vaterite . The aragonite form can be prepared by precipitation at temperatures above 85 °C; the vaterite form can be prepared by precipitation at 60 °C. Calcite contains calcium atoms coordinated by six oxygen atoms; in aragonite they are coordinated by nine oxygen atoms. The vaterite structure
2940-430: Is a chemical compound with the chemical formula Ca CO 3 . It is a common substance found in rocks as the minerals calcite and aragonite , most notably in chalk and limestone , eggshells , gastropod shells , shellfish skeletons and pearls . Materials containing much calcium carbonate or resembling it are described as calcareous . Calcium carbonate is the active ingredient in agricultural lime and
3045-402: Is a common filler material for latex gloves with the aim of achieving maximum saving in material and production costs. Fine ground calcium carbonate (GCC) is an essential ingredient in the microporous film used in diapers and some building films, as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching. GCC and PCC are used as
3150-448: Is about 0.035 kPa. At temperatures above 550 °C the equilibrium CO 2 pressure begins to exceed the CO 2 pressure in air. So above 550 °C, calcium carbonate begins to outgas CO 2 into air. However, in a charcoal fired kiln, the concentration of CO 2 will be much higher than it is in air. Indeed, if all the oxygen in the kiln is consumed in the fire, then
3255-560: Is also favored on the seaward margin of shelves and platforms, where there is upwelling deep ocean water rich in nutrients that increase organic productivity. Reefs are common here, but when lacking, ooid shoals are found instead. Finer sediments are deposited close to shore. The lack of deep sea limestones is due in part to rapid subduction of oceanic crust, but is more a result of dissolution of calcium carbonate at depth. The solubility of calcium carbonate increases with pressure and even more with higher concentrations of carbon dioxide, which
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3360-411: Is also used in the purification of iron from iron ore in a blast furnace . The carbonate is calcined in situ to give calcium oxide , which forms a slag with various impurities present, and separates from the purified iron. In the oil industry , calcium carbonate is added to drilling fluids as a formation-bridging and filtercake-sealing agent; it is also a weighting material which increases
3465-482: Is an uncommon mineral in limestone, and siderite or other carbonate minerals are rare. However, the calcite in limestone often contains a few percent of magnesium . Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from dolomite. Aragonite does not usually contain significant magnesium. Most limestone
3570-403: Is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature drops and pressure increases. Increasing pressure also increases the solubility of calcium carbonate. Calcium carbonate is unusual in that its solubility increases with decreasing temperature. The carbonate compensation depth ranges from 4,000 to 6,000 meters below sea level in modern oceans, and
3675-402: Is carbonate rock, and most of this is limestone. Limestone is found in sedimentary sequences as old as 2.7 billion years. However, the compositions of carbonate rocks show an uneven distribution in time in the geologic record. About 95% of modern carbonates are composed of high-magnesium calcite and aragonite. The aragonite needles in carbonate mud are converted to low-magnesium calcite within
3780-474: Is clusters of peloids cemented together by organic material or mineral cement. Extraclasts are uncommon, are usually accompanied by other clastic sediments, and indicate deposition in a tectonically active area or as part of a turbidity current . The grains of most limestones are embedded in a matrix of carbonate mud. This is typically the largest fraction of an ancient carbonate rock. Mud consisting of individual crystals less than 5 μm (0.20 mils) in length
3885-416: Is commonly white to gray in color. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone an off-white to yellow to red color. The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. The density correspondingly ranges from 1.5 to 2.7 g/cm . Although relatively soft, with
3990-420: Is controlled largely by the amount of dissolved carbon dioxide ( CO 2 ) in the water. This is summarized in the reaction: Increases in temperature or decreases in pressure tend to reduce the amount of dissolved CO 2 and precipitate CaCO 3 . Reduction in salinity also reduces the solubility of CaCO 3 , by several orders of magnitude for fresh water versus seawater. Near-surface water of
4095-545: Is converted to low-magnesium calcite. Diagenesis is the likely origin of pisoliths , concentrically layered particles ranging from 1 to 10 mm (0.039 to 0.394 inches) in diameter found in some limestones. Pisoliths superficially resemble ooids but have no nucleus of foreign matter, fit together tightly, and show other signs that they formed after the original deposition of the sediments. Silicification occurs early in diagenesis, at low pH and temperature, and contributes to fossil preservation. Silicification takes place through
4200-503: Is deposited close to where it formed, classification of limestone is usually based on its grain type and mud content. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera . These organisms secrete structures made of aragonite or calcite, and leave these structures behind when they die. Other carbonate grains composing limestones are ooids , peloids , and limeclasts ( intraclasts and extraclasts [ ca ] ). Skeletal grains have
4305-460: Is described as coquinite . Chalk is a soft, earthy, fine-textured limestone composed of the tests of planktonic microorganisms such as foraminifera, while marl is an earthy mixture of carbonates and silicate sediments. Limestone forms when calcite or aragonite precipitate out of water containing dissolved calcium, which can take place through both biological and nonbiological processes. The solubility of calcium carbonate ( CaCO 3 )
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4410-617: Is described as micrite . In fresh carbonate mud, micrite is mostly small aragonite needles, which may precipitate directly from seawater, be secreted by algae, or be produced by abrasion of carbonate grains in a high-energy environment. This is converted to calcite within a few million years of deposition. Further recrystallization of micrite produces microspar , with grains from 5 to 15 μm (0.20 to 0.59 mils) in diameter. 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
4515-462: 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. Sparite is distinguished from carbonate grains by its lack of internal structure and its characteristic crystal shapes. Geologists are careful to distinguish between sparite deposited as cement and sparite formed by recrystallization of micrite or carbonate grains. Sparite cement
4620-461: Is in the construction industry, either as a building material, or limestone aggregate for road building, as an ingredient of cement , or as the starting material for the preparation of builders' lime by burning in a kiln . However, because of weathering mainly caused by acid rain , calcium carbonate (in limestone form) is no longer used for building purposes on its own, but only as a raw primary substance for building materials. Calcium carbonate
4725-526: Is interest in understanding whether or not it can affect pesticide adsorption and desorption in calcareous soil. Calcium carbonate is a key ingredient in many household cleaning powders like Comet and is used as a scrubbing agent. In 1989, a researcher, Ken Simmons, introduced CaCO 3 into the Whetstone Brook in Massachusetts . His hope was that the calcium carbonate would counter
4830-479: Is later excreted into the dirt. The function of these glands is unknown but is believed to serve as a CO 2 regulation mechanism within the animals' tissues. This process is ecologically significant, stabilizing the pH of acid soils . Beyond Earth, strong evidence suggests the presence of calcium carbonate on Mars . Signs of calcium carbonate have been detected at more than one location (notably at Gusev and Huygens craters). This provides some evidence for
4935-425: Is misleading. Calcium carbonate exists in equilibrium with calcium oxide and carbon dioxide at any temperature. At each temperature there is a partial pressure of carbon dioxide that is in equilibrium with calcium carbonate. At room temperature the equilibrium overwhelmingly favors calcium carbonate, because the equilibrium CO 2 pressure is only a tiny fraction of the partial CO 2 pressure in air, which
5040-404: Is not fully understood. Magnesium carbonate ( MgCO 3 ) has the calcite structure, whereas strontium carbonate ( SrCO 3 ) and barium carbonate ( BaCO 3 ) adopt the aragonite structure, reflecting their larger ionic radii . Calcium carbonate crystallizes in three anhydrous polymorphs , of which calcite is the thermodynamically most stable at room temperature, aragonite
5145-560: Is one of the first minerals to precipitate in marine evaporites. Most limestone is formed by the activities of living organisms near reefs, but the organisms responsible for reef formation have changed over geologic time. For example, stromatolites are mound-shaped structures in ancient limestones, interpreted as colonies of cyanobacteria that accumulated carbonate sediments, but stromatolites are rare in younger limestones. Organisms precipitate limestone both directly as part of their skeletons, and indirectly by removing carbon dioxide from
5250-551: Is only slightly less so, and vaterite is the least stable. The calcite crystal structure is trigonal , with space group R 3 c (No. 167 in the International Tables for Crystallography ), and Pearson symbol hR10. Aragonite is orthorhombic , with space group Pmcn (No 62), and Pearson Symbol oP20. Vaterite is composed of at least two different coexisting crystallographic structures. The major structure exhibits hexagonal symmetry in space group P6 3 /mmc,
5355-473: Is otherwise chemically fairly pure, with clastic sediments (mainly fine-grained quartz and clay minerals ) making up less than 5% to 10% of the composition. Organic matter typically makes up around 0.2% of a limestone and rarely exceeds 1%. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms , or radiolarians ). Fossils are also common in limestone. Limestone
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#17328015398605460-472: Is produced by decaying organic matter settling into the deep ocean that is not removed by photosynthesis in the dark depths. As a result, there is a fairly sharp transition from water saturated with calcium carbonate to water unsaturated with calcium carbonate, the lysocline , which occurs at the calcite compensation depth of 4,000 to 7,000 m (13,000 to 23,000 feet). Below this depth, foraminifera tests and other skeletal particles rapidly dissolve, and
5565-421: Is produced when calcium ions in hard water react with carbonate ions to form limescale . It has medical use as a calcium supplement or as an antacid , but excessive consumption can be hazardous and cause hypercalcemia and digestive issues. Calcium carbonate shares the typical properties of other carbonates . Notably it Calcium carbonate reacts with water that is saturated with carbon dioxide to form
5670-518: Is secondary dolomite, formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock. Limestone has numerous uses: as a chemical feedstock for the production of lime used for cement (an essential component of concrete ), as aggregate for
5775-407: Is the main source of the material lime . It is composed mostly of the minerals calcite and aragonite , which are different crystal forms of CaCO 3 . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in
5880-493: Is then slaked in fresh water to produce a calcium hydroxide suspension for the precipitation of impurities in raw juice during carbonatation . Calcium carbonate in the form of chalk has traditionally been a major component of blackboard chalk. However, modern manufactured chalk is mostly gypsum , hydrated calcium sulfate CaSO 4 ·2H 2 O . Calcium carbonate is a main source for growing biorock . Precipitated calcium carbonate (PCC), pre-dispersed in slurry form,
5985-406: Is used by itself or with additives as a white paint, known as whitewashing . Calcium carbonate is added to a wide range of trade and do it yourself adhesives, sealants, and decorating fillers. Ceramic tile adhesives typically contain 70% to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting stained glass windows, and as
6090-577: Is used therapeutically as phosphate binder in patients on maintenance haemodialysis . It is the most common form of phosphate binder prescribed, particularly in non-dialysis chronic kidney disease. Calcium carbonate is the most commonly used phosphate binder, but clinicians are increasingly prescribing the more expensive, non-calcium-based phosphate binders, particularly sevelamer . Excess calcium from supplements, fortified food, and high-calcium diets can cause milk-alkali syndrome , which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced
6195-739: The Gray Mesa Formation and Atrasado Formation in its western and southern exposures, which extend from the Nacimiento Mountains through the Lucero Uplift to the Los Robles Mountains. For the eastern exposures of the Sandia and Manzano Mountains and Estancia Basin, they recommend division into the Los Moyos Formation and Wild Cow Formation . They recommend abandoning the name Madera Group in
6300-782: The La Pasada Formation and Alamitos Formation in the southern Sangre de Cristo Mountains. In the Manzano Mountains, the Madera has been divided into the Los Moyos , Wild Cow , and Bursum Formations . Another proposed division in the southeastern Sangre de Cristo Mountains is into the Porvenir and Alamitos Formations . Barry Kues and Katherine Giles have recommended the division of the Madera Group into
6405-429: The oceanic crust is subducted under a continental plate sediments will be carried down to warmer zones in the asthenosphere and lithosphere . Under these conditions calcium carbonate decomposes to produce carbon dioxide which, along with other gases, give rise to explosive volcanic eruptions . The carbonate compensation depth (CCD) is the point in the ocean where the rate of precipitation of calcium carbonate
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#17328015398606510-463: The "Sippy regimen" of hourly ingestion of milk and cream, and the gradual addition of eggs and cooked cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in kidney failure , alkalosis , and hypercalcaemia , mostly in men with peptic ulcer disease. These adverse effects were reversed when
6615-462: The 1970s, such liming has been practiced on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly. Calcium carbonate is also used in flue-gas desulfurization applications eliminating harmful SO 2 and NO 2 emissions from coal and other fossil fuels burnt in large fossil fuel power stations. Calcium carbonate is commonly used in
6720-496: The Earth's history. Limestone may have been deposited by microorganisms in the Precambrian , prior to 540 million years ago, but inorganic processes were probably more important and likely took place in an ocean more highly oversaturated in calcium carbonate than the modern ocean. Diagenesis is the process in which sediments are compacted and turned into solid rock . During diagenesis of carbonate sediments, significant chemical and textural changes take place. For example, aragonite
6825-686: The Madera Group to the middle to late Pennsylvanian . In 1903, C.R. Keyes applied the name, Madera limestone , to what he identified as upper Carboniferous beds in the Sandia Mountains. The unit was named for the town of La Madera . The name was subsequently applied to Pennsylvanian marine limestones throughout central and northern New Mexico. D.A. Myers first proposed that the unit be raised to group rank in 1973. The Pennsylvanian stratigraphy of New Mexico has historically been unusually complex and inconsistent, with dozens of names for groups, formations, and members. Kues and Giles recommended that
6930-471: The Madera Group. The exposures near Jemez Springs include some of the richest brachiopod fossil beds in North America. Crinoid stems and bryozoans are also part of the fossil assemblage. The formation is also exposed in the canyon of Rio Grande del Rancho south of Talpa, New Mexico , where brachiopods, crinoids, rugose coral , and graptolite fossils can be found. The fossil assemblage dates
7035-712: The Sandia Formation. It is overlain everywhere by the Abo Formation or its equivalents, with the transition typically gradational, with the base of the Abo placed at the top of the last massive marine limestone bed below the fluvial redbeds typical of the Abo. The transitional zone between the Madera Group and the Abo Formation is sometimes assigned to the Bursum Formation, which is not included in
7140-530: The Sangre de Cristo Mountains. More recently, Spencer G. Lucas and coinvestigators have recommended abandoning the names Los Moyos Formation and Wild Cow Formation and using Grey Mesa Formation and Atrasado Formation throughout the Madera Group. The group is underlain at most locations by the Sandia Formation , with its base typically placed at the first massive marine limestone bed above the shales of
7245-831: The ability to grow all three crystal polymorphs of calcium carbonate, mainly as protection (shells) and muscle attachments. Moreover, they exhibit a remarkable capability of phase selection over calcite and aragonite, and some organisms can switch between the two polymorphs. The ability of phase selection is usually attributed to the use of specific macromolecules or combinations of macromolecules by such organisms. Calcite , aragonite and vaterite are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include limestone , chalk , marble and travertine . Eggshells , snail shells and most seashells are predominantly calcium carbonate and can be used as industrial sources of that chemical. Oyster shells have enjoyed recent recognition as
7350-438: The acid in the stream from acid rain and save the trout that had ceased to spawn. Although his experiment was a success, it did increase the amount of aluminium ions in the area of the brook that was not treated with the limestone. This shows that CaCO 3 can be added to neutralize the effects of acid rain in river ecosystems. Currently calcium carbonate is used to neutralize acidic conditions in both soil and water. Since
7455-434: The base of roads, as white pigment or filler in products such as toothpaste or paint, as a soil conditioner , and as a popular decorative addition to rock gardens . Limestone formations contain about 30% of the world's petroleum reservoirs . Limestone is composed mostly of the minerals calcite and aragonite , which are different crystal forms of calcium carbonate ( CaCO 3 ). Dolomite , CaMg(CO 3 ) 2 ,
7560-657: The beds. This may include the formation of vugs , which are crystal-lined cavities within the limestone. Diagenesis may include conversion of limestone to dolomite by magnesium-rich fluids. There is considerable evidence of replacement of limestone by dolomite, including sharp replacement boundaries that cut across bedding. The process of dolomitization remains an area of active research, but possible mechanisms include exposure to concentrated brines in hot environments ( evaporative reflux ) or exposure to diluted seawater in delta or estuary environments ( Dorag dolomitization ). However, Dorag dolomitization has fallen into disfavor as
7665-480: The bottom with the concave face downwards. This traps a void space that can later be filled by sparite. Geologists use geopetal structures to determine which direction was up at the time of deposition, which is not always obvious with highly deformed limestone formations. The cyanobacterium Hyella balani can bore through limestone; as can the green alga Eugamantia sacculata and the fungus Ostracolaba implexa . Calcium carbonate Calcium carbonate
7770-563: The calcium in cow's milk . Calcium carbonate is also used as a firming agent in many canned and bottled vegetable products. Several calcium supplement formulations have been documented to contain the chemical element lead , posing a public health concern. Lead is commonly found in natural sources of calcium. Agricultural lime , powdered chalk or limestone, is used as a cheap method of neutralising acidic soil , making it suitable for planting, also used in aquaculture industry for pH regulation of pond soil before initiating culture. There
7875-414: The density of drilling fluids to control the downhole pressure. Calcium carbonate is added to swimming pools , as a pH corrector for maintaining alkalinity and offsetting the acidic properties of the disinfectant agent. It is also used as a raw material in the refining of sugar from sugar beet ; it is calcined in a kiln with anthracite to produce calcium oxide and carbon dioxide. This burnt lime
7980-466: The depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles, based on criteria such as whether the grains were originally in mutual contact, and therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of
8085-469: The deposits are highly porous, so that they have a spongelike texture, they are typically described as tufa . Secondary calcite deposited by supersaturated meteoric waters ( groundwater ) in caves is also sometimes described as travertine. This produces speleothems , such as stalagmites and stalactites . Coquina is a poorly consolidated limestone composed of abraded pieces of coral , shells , or other fossil debris. When better consolidated, it
8190-406: The earth's oceans are oversaturated with CaCO 3 by a factor of more than six. The failure of CaCO 3 to rapidly precipitate out of these waters is likely due to interference by dissolved magnesium ions with nucleation of calcite crystals, the necessary first step in precipitation. Precipitation of aragonite may be suppressed by the presence of naturally occurring organic phosphates in
8295-399: The first refers to the grains and the second to the cement. For example, a limestone consisting mainly of ooids, with a crystalline matrix, would be termed an oosparite. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample. Robert J. Dunham published his system for limestone in 1962. It focuses on
8400-431: The formation of calcite and/or promote the nucleation of aragonite. For example, the formation of aragonite is promoted by the presence of magnesium ions, or by using proteins and peptides derived from biological calcium carbonate. Some polyamines such as cadaverine and Poly(ethylene imine) have been shown to facilitate the formation of aragonite over calcite. Organisms, such as molluscs and arthropods , have shown
8505-572: The formation of distinctive minerals from the silica and clay present in the original limestone. Two major classification schemes, the Folk and Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks . Based on composition, there are three main components: allochems (grains), matrix (mostly micrite), and cement (sparite). The Folk system uses two-part names;
8610-429: The geologic record are called bioherms . Many are rich in fossils, but most lack any connected organic framework like that seen in modern reefs. The fossil remains are present as separate fragments embedded in ample mud matrix. Much of the sedimentation shows indications of occurring in the intertidal or supratidal zones, suggesting sediments rapidly fill available accommodation space in the shelf or platform. Deposition
8715-417: The least stable polymorph crystallizes first, followed by the crystallization of different polymorphs via a sequence of increasingly stable phases. However, aragonite, whose stability lies between those of vaterite and calcite, seems to be the exception to this rule, as aragonite does not form as a precursor to calcite under ambient conditions. Aragonite occurs in majority when the reaction conditions inhibit
8820-468: The microscopic level. However, it also leaves specimens vulnerable to weathering when exposed to the surface. Trilobite populations were once thought to have composed the majority of aquatic life during the Cambrian , due to the fact that their calcium carbonate-rich shells were more easily preserved than those of other species, which had purely chitinous shells. The main use of calcium carbonate
8925-469: The mineral dolomite , CaMg(CO 3 ) 2 . Magnesian limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite ( dolomitic limestone ), or for any other limestone containing a significant percentage of magnesium . Most limestone was formed in shallow marine environments, such as continental shelves or platforms , though smaller amounts were formed in many other environments. Much dolomite
9030-464: The minor structure is still unknown. All three polymorphs crystallize simultaneously from aqueous solutions under ambient conditions. In additive-free aqueous solutions, calcite forms easily as the major product, while aragonite appears only as a minor product. At high saturation, vaterite is typically the first phase precipitated, which is followed by a transformation of the vaterite to calcite. This behavior seems to follow Ostwald's rule , in which
9135-533: The name Madera Group be applied to similar exposures of shelf and marginal basin beds of Desmoinean (upper Moscovian ) to early Virgilian age found from north-central and central New Mexico south along the west side of the Orogrande Basin as far as the Caballo and Robledo Mountains . Limestones Limestone ( calcium carbonate CaCO 3 ) is a type of carbonate sedimentary rock which
9240-410: The ocean basins, but limestone is rarely preserved in continental slope and deep sea environments. The best environments for deposition are warm waters, which have both a high organic productivity and increased saturation of calcium carbonate due to lower concentrations of dissolved carbon dioxide. Modern limestone deposits are almost always in areas with very little silica-rich sedimentation, reflected in
9345-403: The partial pressure of CO 2 in the kiln can be as high as 20 kPa. The table shows that this partial pressure is not achieved until the temperature is nearly 800 °C. For the outgassing of CO 2 from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of CO 2 . And for it to happen rapidly,
9450-440: The past presence of liquid water. Carbonate is found frequently in geologic settings and constitutes an enormous carbon reservoir . Calcium carbonate occurs as aragonite , calcite and dolomite as significant constituents of the calcium cycle . The carbonate minerals form the rock types: limestone , chalk , marble , travertine , tufa , and others. In warm, clear tropical waters corals are more abundant than towards
9555-446: The plastic industry as a filler. When it is incorporated in a plastic material, it can improve the hardness, stiffness, dimensional stability and processability of the material. Calcination of limestone using charcoal fires to produce quicklime has been practiced since antiquity by cultures all over the world. The temperature at which limestone yields calcium oxide is usually given as 825 °C, but stating an absolute threshold
9660-492: The poles where the waters are cold. Calcium carbonate contributors, including plankton (such as coccoliths and planktic foraminifera ), coralline algae , sponges , brachiopods , echinoderms , bryozoa and mollusks , are typically found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate. The calcification processes are changed by ocean acidification . Where
9765-426: The reaction: Fossils are often preserved in exquisite detail as chert. Cementing takes place rapidly in carbonate sediments, typically within less than a million years of deposition. Some cementing occurs while the sediments are still under water, forming hardgrounds . Cementing accelerates after the retreat of the sea from the depositional environment, as rainwater infiltrates the sediment beds, often within just
9870-657: The regimen stopped, but it was fatal in some patients with protracted vomiting. Milk-alkali syndrome declined in men after effective treatments for peptic ulcer disease arose. Since the 1990s it has been most frequently reported in women taking calcium supplements above the recommended range of 1.2 to 1.5 grams daily, for prevention and treatment of osteoporosis, and is exacerbated by dehydration . Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake. Excessive calcium intake can lead to hypercalcemia, complications of which include vomiting, abdominal pain and altered mental status. As
9975-482: The relative purity of most limestones. Reef organisms are destroyed by muddy, brackish river water, and carbonate grains are ground down by much harder silicate grains. Unlike clastic sedimentary rock, limestone is produced almost entirely from sediments originating at or near the place of deposition. Limestone formations tend to show abrupt changes in thickness. Large moundlike features in a limestone formation are interpreted as ancient reefs , which when they appear in
10080-555: The relatively low hardness level of 3 on the Mohs scale , and will therefore not scratch glass and most other ceramics , enamel , bronze , iron , and steel , and have a moderate effect on softer metals like aluminium and copper . A paste made from calcium carbonate and deionized water can be used to clean tarnish on silver . Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement for gastric antacid (such as Tums and Eno ). It may be used as
10185-460: The rock. The Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright (1992). It adds some diagenetic patterns to the classification scheme. Travertine is a term applied to calcium carbonate deposits formed in freshwater environments, particularly waterfalls , cascades and hot springs . Such deposits are typically massive, dense, and banded. When
10290-410: The sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite , a closely related rock, which contains a high percentage of
10395-479: The sediments increases. Chemical compaction takes place by pressure solution of the sediments. This process dissolves minerals from points of contact between grains and redeposits it in pore space, reducing the porosity of the limestone from an initial high value of 40% to 80% to less than 10%. Pressure solution produces distinctive stylolites , irregular surfaces within the limestone at which silica-rich sediments accumulate. These may reflect dissolution and loss of
10500-662: The sediments of the ocean floor abruptly transition from carbonate ooze rich in foraminifera and coccolith remains ( Globigerina ooze) to silicic mud lacking carbonates. In rare cases, turbidites or other silica-rich sediments bury and preserve benthic (deep ocean) carbonate deposits. Ancient benthic limestones are microcrystalline and are identified by their tectonic setting. Fossils typically are foraminifera and coccoliths. No pre-Jurassic benthic limestones are known, probably because carbonate-shelled plankton had not yet evolved. Limestones also form in freshwater environments. These limestones are not unlike marine limestone, but have
10605-480: The soluble calcium bicarbonate . This reaction is important in the erosion of carbonate rock , forming caverns , and leads to hard water in many regions. An unusual form of calcium carbonate is the hexahydrate ikaite , CaCO 3 ·6H 2 O . Ikaite is stable only below 8 °C. The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (such as for food or pharmaceutical use), can be produced from
10710-502: The various polymorphs (calcite, aragonite) have different compensation depths based on their stability. Calcium carbonate can preserve fossils through permineralization . Most of the vertebrate fossils of the Two Medicine Formation —a geologic formation known for its duck-billed dinosaur eggs—are preserved by CaCO 3 permineralization. This type of preservation conserves high levels of detail, even down to
10815-533: The water by photosynthesis and thereby decreasing the solubility of calcium carbonate. Limestone shows the same range of sedimentary structures found in other sedimentary rocks. However, finer structures, such as lamination , are often destroyed by the burrowing activities of organisms ( bioturbation ). Fine lamination is characteristic of limestone formed in playa lakes , which lack the burrowing organisms. Limestones also show distinctive features such as geopetal structures , which form when curved shells settle to
10920-553: The water. Although ooids likely form through purely inorganic processes, the bulk of CaCO 3 precipitation in the oceans is the result of biological activity. Much of this takes place on carbonate platforms . The origin of carbonate mud, and the processes by which it is converted to micrite, continue to be a subject of research. Modern carbonate mud is composed mostly of aragonite needles around 5 μm (0.20 mils) in length. Needles of this shape and composition are produced by calcareous algae such as Penicillus , making this
11025-416: Was likely deposited in pore space between grains, suggesting a high-energy depositional environment that removed carbonate mud. Recrystallized sparite is not diagnostic of depositional environment. Limestone outcrops are recognized in the field by their softness (calcite and aragonite both have a Mohs hardness of less than 4, well below common silicate minerals) and because limestone bubbles vigorously when
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