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79-463: It is found on limestone soils in southern France and around the Mediterranean Basin , generally near the seacoast where the moderated Mediterranean climate provides annual summer drought . It is an anthropogenic degradation and succession form of former evergreen oak forests that existed until around 2500 years BCE. The term has also found its way into haute cuisine , suggestive of

158-455: 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

237-457: 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

316-454: A charm and worked into bridal bouquets . Heather stalks are used by a small industry in Scotland as a raw material for sentimental jewellery. The stalks are stripped of bark, dyed in bright colours and then compressed with resin. Calluna vulgaris herb has been used in the traditional Austrian medicine internally as tea for treatment of disorders of the kidneys and urinary tract. Heather

395-434: 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

474-612: 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

553-449: 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

632-458: A characteristic strong taste, and an unusual texture, for it is thixotropic , being a jelly until stirred, when it becomes a syrup like other honey, but then sets again to a jelly. This makes the extraction of the honey from the comb difficult, and it is therefore often sold as comb honey . White heather is regarded in Scotland as being lucky, a tradition brought from Balmoral to England by Queen Victoria and sprigs of it are often sold as

711-949: 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

790-412: 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

869-483: 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

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948-621: 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

1027-455: 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

1106-435: 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

1185-466: 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

1264-525: 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

1343-523: 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

1422-594: A mixture of flavourings used in the brewing of heather-beer during the Middle Ages before the use of hops . Thomas Pennant wrote in A Tour in Scotland (1769) that on the Scottish island of Islay "ale is frequently made of the young tops of heath, mixing two thirds of that plant with one of malt, sometimes adding hops". "Heath Beer" is mentioned in the recipe book of Lady Ann Fanshawe (compiled from 1651). From time immemorial heather has been used for making besoms ,

1501-448: 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

1580-420: A practice recorded in " Buy Broom Buzzems " a song probably written by William Purvis (Blind Willie) (1752–1832) from Newcastle-upon-Tyne , England. Heather honey is a highly valued product in moorland and heathland areas, with many beehives being moved there in late summer. Not always as valued as it is today, it was dismissed as mel improbum , "unwholesome honey" by Dioscurides . Heather honey has

1659-449: 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

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1738-676: A similar Mediterranean climate ecoregion is named chaparral ; in Chile it is named the matorral ; in South Africa it is named fynbos ; and in Australia it is named mallee . All are in the Mediterranean forests, woodlands, and scrub biome. Both garrigue and maquis are associated with the Mediterranean climate within the Mediterranean region . However, the distinction is not clear and term use

1817-409: A wide range of purples, and including reds. The flowering season with different cultivars extends from late July to November in the northern hemisphere. The flowers may turn brown but still remain on the plants over winter, and this can lead to interesting decorative effects. Cultivars with ornamental foliage are usually selected for reddish and golden leaf colour. A few forms can be silvery grey. Many of

1896-560: 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

1975-482: 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

2054-402: 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

2133-474: 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

2212-416: 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

2291-420: 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

2370-545: 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

2449-503: 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

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2528-460: 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 )

2607-617: 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

2686-650: Is differentiated from Erica by its corolla and calyx each being in four parts instead of five. Calluna vulgaris is native to Europe , Iceland , the Faroe Islands , and the Azores . It has been introduced into many other places worldwide with suitable climates, including North America , Australia , New Zealand and the Falkland Islands . It is extremely cold- hardy , surviving severe exposure and freezing conditions well below −20 °C (−4 °F). The plant

2765-462: 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

2844-440: Is inconsistent. Maquis shrubland is broadly similar to garrigue, but the vegetation is denser, being composed of numerous closely spaced shrubs. Maquis is associated with siliceous (acid) soils, unlike the relatively alkaline calcareous soils of the garrigue. Its plant communities are often suites associated with holm oak . Calcifuges such as Erica and Calluna are present in the maquis ecoregion . Deforestation of

2923-555: Is often extensive. It is associated with limestone and base rich soils, and calcium associated plants. Aside from dense thickets of kermes oak that punctuate the garrigue landscape, juniper and stunted holly oaks and holm oaks are the typical trees; aromatic lime-tolerant shrubs such as lavender , sage , rosemary , wild thyme and Artemisia are common garrigue plants. The aromatic oils and soluble monoterpenes of such herbs leached into garrigue soils from leaf litter have been connected with plant allelopathy , which asserts

3002-560: 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

3081-473: 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

3160-472: 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

3239-514: 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

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3318-425: Is seen as iconic of Scotland , where the plant grows widely. When poems like Bonnie Auld Scotland speak of "fragrant hills of purple heather', when the hero of Kidnapped flees through the heather, when heather and Scotland are linked in the same sentence, the heather talked about is Calluna vulgaris . Purple heather is one of the two national flowers of Norway , the other being Saxifraga cotyledon . It

3397-407: 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

3476-538: Is the sole species in the genus Calluna in the flowering plant family Ericaceae . It is a low-growing evergreen shrub growing to 20 to 50 centimetres (8 to 20 in) tall, or rarely to 1 metre (40 in) and taller, and is found widely in Europe and Asia Minor on acidic soils in open sunny situations and in moderate shade. It is the dominant plant in most heathland and moorland in Europe, and in some bog vegetation and acidic pine and oak woodland. It

3555-561: Is tolerant of grazing and regenerates following occasional burning, and is often managed in nature reserves and grouse moors by sheep or cattle grazing, and also by light burning. Calluna has small-scale leaves (less than 2–3 mm long) borne in opposite and decussate pairs, whereas those of Erica are generally larger and in whorls of 3–4, sometimes 5. It flowers from July to September. In wild plants these are normally mauve , but white-flowered plants also occur occasionally. They are terminal in racemes with sepal-like bracts at

3634-479: The garrigues region of France are said to produce wines with a "barnyard" or "earthy" tone, or "the herbal scent of lavender that fills the hills of Provence in the summer time." Some wines bottled in Southern France contain the word garrigues as part of their appellation or label name. Limestone Limestone ( calcium carbonate CaCO 3 ) is a type of carbonate sedimentary rock which

3713-496: 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

3792-434: 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 ,

3871-419: The base with a superior ovary, the fruit a capsule . Unlike Erica , Calluna sometimes sports double flowers . Calluna is sometimes referred to as Summer (or Autumn) heather to distinguish it from winter or spring flowering species of Erica . Phenolic compounds in the shoots of Calluna vulgaris include chlorogenic acid and a novel phenolic glycoside, most of which are found in greater number during

3950-657: 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

4029-520: 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 . Calluna Calluna vulgaris , common heather , ling , or simply heather ,

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4108-892: The decline of goat-pasturing. First cited in French in 1546, garrigue is borrowed from Provençal garriga, equivalent to Old French jarrie . The term is most likely related to Gascon carroc "rock" and to Germanic Swiss Karren , a kind of sedimentary rock . These words could derive from a supposed source such as *carra "rock," perhaps a remnant of a pre-Roman language and possibly akin to Basque *karr- , harri "rock." Gaulish and then Latin appear to have borrowed *carra , which evolved into its modern descendants in Romance languages . The dense, thrifty growth of garrigue flora has recommended many of its shrubs and sub-shrubs for uses as ornamental plants in traditional and drought tolerant gardens . Many shrubs and flowering perennials of

4187-462: 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

4266-469: 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

4345-423: The dominance of a plant over its neighbors, especially annuals , and contributes to the characteristic open spacing and restricted flora in a garrigue. The fines (charred wood and smoke residues, or charcoal dust) of periodic brush fires also have had an effect on the patterning and composition of the garrigues. Clear summer skies and intense solar radiation have induced the evolution of protective physiologies:

4424-406: 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

4503-822: The familiar glaucous, grayish-green of garrigue landscapes is produced by the protective white hairs and light-diffusing, pebbled surfaces of many leaves typical of garrigue plants. Garrigue is a common general word for the shrubland habitat ecosystems in southern France along with maquis , which are known elsewhere in the Mediterranean region as matorral and tomillar in Spain, macchia in Italy, phrygana in Greece, garig in Croatia, and batha in Palestine or horesh in Israel . In California

4582-399: 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

4661-572: 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;

4740-652: The garrigue are mainstays of the English "mixed border" of herbaceous and woody plants found in English gardens , and around the world, though often grown under cooler, moister conditions. Some have become invasive species in the Mediterranean forests, woodlands, and scrub biome's other ecoregions beyond the Mediterranean Basin on other continents, including the California chaparral and woodlands . Grapes that are grown in

4819-429: 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

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4898-485: The indigenous oak forest since the Late Bronze Age , for cultivation of olives , vines and grain, the introduction of sheep and especially goats and charcoal-making for heat and iron-working, exposed the land surface to weathering and resulted in erosion of the topsoil. The wild garrigue, then, is a man-formed landscape. The intensity of grazing pressure has had a direct response in the ecotope , reflected today in

4977-469: 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

5056-410: 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

5135-533: The ornamental foliage forms change colour with the onset of winter weather, usually increasing in intensity of colour. Some forms are grown for distinctive young spring foliage. The following cultivars have gained the Royal Horticultural Society 's Award of Garden Merit : Heather is an important food source for various sheep and deer which can graze the tips of the plants when snow covers low-growing vegetation. Willow grouse and red grouse feed on

5214-426: 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

5293-482: 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

5372-436: The resinous flavours of a garrigue shrubland . UNEP World Conservation Monitoring Centre described garrigue as "discontinuous bushy associations of the Mediterranean calcareous plateaus , which have relatively alkaline soils . It is often composed of kermes oak , lavender , thyme , and white cistus . There may be a few isolated trees." Garrigue is discontinuous with widely spaced bush associations with open spaces, and

5451-460: 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

5530-410: 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

5609-479: 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

5688-662: 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

5767-426: The summer. The nectar of Calluna vulgaris contains a megastigmane, callunene, that is inhibitory at naturally occurring concentrations to a common trypanosome parasite of bumble bees, Crithidia bombi . Koch et al. elucidate the mechanism of activity that results in the loss of the parasite's flagellum, leading to reduced infectivity, because the flagellum is crucial to anchoring in the insect gut. Calluna

5846-533: 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

5925-553: 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

6004-419: The young shoots and seeds of this plant. Both adult and larva of the heather beetle ( Lochmaea suturalis ) feed on it, and can cause extensive mortality in some instances. The larvae of a number of Lepidoptera species also feed on the plant, notably the small emperor moth Saturnia pavonia . Formerly heather was used to dye wool yellow and to tan leather. With malt , heather is an ingredient in gruit ,

6083-798: Was introduced to New Zealand and has become an invasive weed in some areas, notably the Tongariro National Park and Mount Ruapehu in the North Island, as well as the Wilderness Reserve (Te Anau) in the South Island, overgrowing native plants. Heather beetles have been released to stop the heather, with preliminary trials successful to date. There are many named cultivars , selected for variation in flower colour and for different foliage colour and growing habits. Different cultivars have flower colours ranging from white, through pink and

6162-416: 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

6241-475: Was separated from the closely related genus Erica by Richard Anthony Salisbury , who devised the generic name Calluna probably from the Ancient Greek Kallyno ([καλλύνω] Error: {{Transliteration}}: transliteration text not Latin script (pos 1) ( help ) ), "beautify, sweep clean", in reference to its traditional use in besoms . The specific epithet vulgaris is Latin for 'common'. Calluna

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