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52-457: The Magnesian Limestone is a suite of carbonate rocks in north-east England dating from the Permian period. The outcrop stretches from Nottingham northwards through Yorkshire and into County Durham where it is exposed along the coast between Hartlepool and South Shields . The term has now been discontinued in formal use though it appears widely in popular and scientific literature on

104-441: A beach empty and clean, the animal having already died. Empty seashells are often picked up by beachcombers. However, the majority of seashells which are offered for sale commercially have been collected alive (often in bulk) and then killed and cleaned, specifically for the commercial trade. This type of large-scale exploitation can sometimes have a strong negative impact on local ecosystems , and sometimes can significantly reduce

156-441: A few live animals, most responsible collectors do not often over-collect or otherwise disturb ecosystems. The study of the entire molluscan animal (as well as the shell) is known as malacology ; a person who studies mollusks is known as a malacologist . Seashells are commonly found in beach drift, which is natural detritus deposited along strandlines on beaches by the waves and the tides . Shells are very often washed up onto

208-473: A few titles on this subject in the US, see the list of books at the foot of this article.) Identifications to the species level are generally achieved by examining illustrations and written descriptions, rather than by the use of Identification keys , as is often the case in identifying plants and other phyla of invertebrates. The construction of functional keys for the identification of the shells of marine mollusks to

260-501: A flexible hinge. The animal's body is held protectively inside these two shells. Bivalves that do not have two shells either have one shell or they lack a shell altogether. The shells are made of calcium carbonate and are formed in layers by secretions from the mantle. Bivalves, also known as pelecypods, are mostly filter feeders; through their gills, they draw in water, in which is trapped tiny food particles. Some bivalves have eyes and an open circulatory system. Bivalves are used all over

312-462: A gastropod seashell is a reference to the sacred chank shell Turbinella pyrum of India. In 2003, Maggi Hambling designed a striking 13 ft (4 m) high sculpture of a scallop shell which stands on the beach at Aldeburgh , in England. The goddess of love, Venus or Aphrodite , is often traditionally depicted rising from the sea on a seashell. In The Birth of Venus , Botticelli depicted

364-422: A girdle, usually come apart not long after death, so they are almost always found as disarticulated plates. Plates from larger species of chitons are sometimes known as "butterfly shells" because of their shape. Only a few species of cephalopods have shells (either internal or external) that are sometimes found washed up on beaches. Some cephalopods such as Sepia , the cuttlefish, have a large internal shell,

416-409: A hard "test" or shell. After the animal dies, the flesh rots out and the spines fall off, and then fairly often the empty test washes up whole onto a beach, where it can be found by a beachcomber. These tests are fragile and easily broken into pieces. The brachiopods , or lamp shells, superficially resemble clams, but the phylum is not closely related to mollusks. Most lines of brachiopods ended during

468-431: A major natural history or zoology museum at some point, however, shells with little or no collecting data are usually of no value to science, and are likely not to be accepted by a major museum. Apart from any damage to the shell that may have happened before it was collected, shells can also suffer damage when they are stored or displayed. For an example of one rather serious kind of damage see Byne's disease . There are

520-616: A medium of exchange in various places, including many Indian Ocean and Pacific Ocean islands, also in North America, Africa and the Caribbean. Seashells have often been used as tools , because of their strength and the variety of their shapes. Because seashells are in some areas a readily available bulk source of calcium carbonate, shells such as oyster shells are sometimes used as soil conditioners in horticulture . The shells are broken or ground into small pieces in order to have

572-457: A number of books about land and freshwater mollusks, the majority of popular books emphasize, or focus exclusively on, the shells of marine mollusks. Both the science of studying mollusk shells and the hobby of collecting and classifying them are known as conchology . The line between professionals and amateur enthusiasts is often not well defined in this subject, because many amateurs have contributed to, and continue to contribute to, conchology and

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624-522: A number of clubs or societies which consist of people who are united by a shared interest in shells. In the US, these clubs are more common in southerly coastal areas, such as Florida and California , where the marine fauna is rich in species. Seashells are usually identified by consulting general or regional shell-collecting field guides , and specific scientific books on different taxa of shell-bearing mollusks ( monographs ) or "iconographies" (limited text – mainly photographs or other illustrations). (For

676-433: A sturdy, and usually readily available, "free" resource which is often easily found on beaches, in the intertidal zone , and in the shallow subtidal zone. As such they are sometimes used second-hand by animals other than humans for various purposes, including for protection (as in hermit crabs ) and for construction. There are numerous popular books and field guides on the subject of shell-collecting. Although there are

728-461: A wooden (usually octagonal) hinged box-frame. The patterns used often featured heart-shaped designs, or included a sentimental expression of love spelled out in small shells. The making of shell work artifacts is a practice of Aboriginal women from La Perouse in Sydney , dating back to the 19th century. Shell work objects include baby shoes, jewelry boxes and replicas of famous landmarks, including

780-402: Is doloimite which contains significant trace levels of iron. Due to the similar ionic radii of iron(II) and magnesium , iron(II) can easily substitute magnesium to form ferroan dolomite; manganese can also substitute this atom. The result can be defined as ankerite . The exact delineation between which minerals are considered ferroan dolomite and which are ankerite is unclear. Ankerite with

832-433: Is dolomite which has more calcium than magnesium in its mineral form. This is the most common form of dolomite found naturally and artificially from synthesis . This dolomite, when formed in the oceans, can prove to be metastable . The resultant structure of this mineral presents minimal differences from regular dolomite likely as a result of formation after initial crystal growth. Iron-rich dolomite, or ferroan dolomite,

884-465: Is done in paleoclimatology . Carbonate rocks can also be used for understanding various other systems as described below. Limestone is the most common carbonate rock and is a sedimentary rock made of calcium carbonate with two main polymorphs : calcite and aragonite. While the chemical composition of these two minerals is the same, their physical properties differ significantly due to their different crystalline form . The most common form found in

936-938: The International Commission on Zoological Nomenclature (ICZN). Large numbers of new species are published in the scientific literature each year. There are currently an estimated 100,000 species of mollusks worldwide. The term seashell is also applied loosely to mollusk shells that are not of marine origin, for example by people walking the shores of lakes and rivers using the term for the freshwater mollusk shells they encounter. Seashells purchased from tourist shops or dealers may include various freshwater and terrestrial shells as well. Non-marine items offered may include large and colorful tropical land snail shells, freshwater apple snail shells, and pearly freshwater unionid mussel shells. This can be confusing to collectors, as non-marine shells are often not included in their reference books. Seashells have been used as

988-483: The Permian-Triassic extinction event , and their ecological niche was filled by bivalves. A few of the remaining species of brachiopods occur in the low intertidal zone and thus can be found live by beachcombers. Some polychaetes , marine annelid worms in the family Serpulidae , secrete a hard tube made of calcium carbonate, adhering to stones or other shells. This tube resembles, and can be confused with,

1040-716: The Sydney Harbour Bridge and the Sydney Opera House . The shellwork tradition began as an Aboriginal women's craft which was adapted and tailored to suit the tourist souvenir market, and which is now considered high art. Small pieces of colored and iridescent shell have been used to create mosaics and inlays , which have been used to decorate walls, furniture and boxes. Large numbers of whole seashells, arranged to form patterns, have been used to decorate mirror frames, furniture and human-made shell grottos . A very large outdoor sculpture at Akkulam of

1092-400: The cuttlefish bone , and this often washes up on beaches in parts of the world where cuttlefish are common. Spirula spirula is a deep water squid-like cephalopod. It has an internal shell which is small (about 1 in or 24 mm) but very light and buoyant. This chambered shell floats very well and therefore washes up easily and is familiar to beachcombers in the tropics. Nautilus is

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1144-544: The greenhouse effect . There is significant amount of research studying the ideal quantity of calcium carbonate (derived from limestone) in concrete and if other compounds can be used to provide the same economic and structural integrity benefits. Many forms of paleoclimatology exist whereby carbonate rocks can be used to determine past climate. Corals and sediments are well-known proxies for these reconstructions. Corals are marine organisms with calcium carbonate skeletons (rocks) which grow specific to oceanic conditions at

1196-503: The "pure" CaFe(CO 3 ) 2 chemical formula has yet to be found in nature . Carbonate rocks are significant for both human understanding of Earth's atmospheric and geologic history, in addition to providing humans with significant resources for current civilizational endeavors such as concrete . Limestone is often used in concrete as powder due to its cheap cost. During the formation of concrete, however, breakdown of limestone releases carbon dioxide and contributes significantly to

1248-693: The Seaham Residue. Much of the Magnesian Limestone is dolomite , i.e. calcium magnesium carbonate, and has been for many years the main source of dolomite-rock in Britain. It is used in connection with the production of refractory bricks but also for aggregate for road-building and other construction purposes. It is also used in the production of agricultural lime. This type of limestone was used for statues in antiquity because of its resistance to acid. Many pieces of dolomite were found in

1300-597: The animal has died and the soft parts have decomposed or been eaten by another organism. A seashell is usually the exoskeleton of an invertebrate (an animal without a backbone), and is typically composed of calcium carbonate or chitin. Most shells that are found on beaches are the shells of marine mollusks, partly because these shells are usually made of calcium carbonate, and endure better than shells made of chitin. Apart from mollusk shells , other shells that can be found on beaches are those of barnacles , horseshoe crabs and brachiopods . Marine annelid worms in

1352-469: The aragonite of coral skeleton can be used, alongside other proxies like oxygen isotopic ratios , to reconstruct climate variability when the coral was growing. This is because Strontium will sometimes substitute for Calcium in the calcium carbonate molecule depending on temperature effects. Similar to the concept for using compositional changes in coral skeletons as proxies for climate conditions, compositional changes in marine sediments can be used for

1404-504: The class Malacostraca (crabs, shrimps and lobsters, for instance), the plates of the exoskeleton may be fused to form a more or less rigid carapace . Moulted carapaces of a variety of marine malacostraceans often wash up on beaches. The horseshoe crab is an arthropod of the family Limulidae . The shells or exuviae of these arachnid relatives are common in beach drift in certain areas of the world. Some echinoderms such as sea urchins , including heart urchins and sand dollars , have

1456-399: The desired effect of raising the pH and increasing the calcium content in the soil. Seashells have played a part in religion and spirituality, sometimes even as ritual objects. Seashells have been used as musical instruments, wind instruments for many hundreds if not thousands of years. Most often the shells of large sea snails are used, as trumpets, by cutting a hole in the spire of

1508-421: The distribution of rare species . Seashells are created by the molluscs that use them for protection. Molluscs have an outside layer of tissues on their bodies – the mantle – which creates the shell material and which connects the shell to the mollusc. The specialized cells in the mantle form the shell using different minerals and proteins . The proteins are then used to create the framework that supports

1560-529: The existing rock grains together or it can fill fractures. Compared to calcite, aragonite is less stable and more soluble , and can thus be converted to calcite under certain conditions. In solution, magnesium ions can act as promoters of aragonite growth as they inhibit calcite precipitation . Often this inhibited precipitation occurs in biology where organisms aim to precipitate calcium carbonate for their structural features such as for skeleton and shells . The discovery of dolomite rock, or dolostone ,

1612-426: The family Serpulidae create shells which are tubes made of calcium carbonate cemented onto other surfaces. The shells of sea urchins are called " tests ", and the moulted shells of crabs and lobsters are exuviae . While most seashells are external, some cephalopods have internal shells. Seashells have been used by humans for many different purposes throughout history and prehistory. However, seashells are not

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1664-541: The geology of northern England. The Magnesian Limestone is now incorporated within the Zechstein Group . In the southern part of its outcrop, the former 'Lower Magnesian Limestone' is now referred to as the ' Cadeby Formation '. Overlying this it is the 'Edlington Formation' (formerly the ' Middle Permian Marl') and above this the Brotherton Formation (formerly the 'Upper Magnesian Limestone'). In

1716-401: The goddess Venus rising from the ocean on a scallop shell. Sea shells found in the creek and backwater of the coast of west India are used as an additive to poultry feed. They are crushed and mixed with jowar maize and dry fish. Seashells, namely from bivalves and gastropods, are fundamentally composed of calcium carbonate. In this sense, they have potential to be used as raw material in

1768-527: The growing shell. Calcium carbonate is the main compound of shell structure, aiding in adhesion . The word seashell is often used to mean only the shell of a marine mollusk . Marine mollusk shells that are familiar to beachcombers and thus most likely to be called "seashells" are the shells of marine species of bivalves (or clams ), gastropods (or snails ), scaphopods (or tusk shells ), polyplacophorans (or chitons ), and cephalopods (such as nautilus and spirula ). These shells are very often

1820-658: The larger science of malacology . Many shell collectors belong to "shell clubs" where they can meet others who share their interests. A large number of amateurs collect the shells of marine mollusks, and this is partly because many shells wash up empty on beaches, or live in the intertidal or sub-tidal zones, and are therefore easily found and preserved without much in the way of specialized equipment or expensive supplies. Some shell collectors find their own material and keep careful records, or buy only "specimen shells", which means shells which have full collecting data : information including how, when, where, in what habitat, and by whom,

1872-414: The most common seashells that wash up on large sandy beaches or in sheltered lagoons . They can sometimes be extremely numerous. Very often the two valves become separated. There are more than 15,000 species of bivalves that live in both marine and freshwater. Examples of bivalves are clams, scallops, mussels, and oysters. The majority of bivalves consist of two identical shells that are held together by

1924-399: The most commonly encountered, both in the wild, and for sale as decorative objects. Marine species of gastropods and bivalves are more numerous than land and freshwater species, and the shells are often larger and more robust. The shells of marine species also often have more sculpture and more color, although this is by no means always the case. In the tropical and sub-tropical areas of

1976-934: The north, the Lower Magnesian Limestone is now referred to as the Raisby Formation and the middle Magnesian Limestone as the Ford Formation. The Upper Magnesian Limestone is replaced by the Roker Formation (in its lower part) and the Seaham Formation (in its upper part) with the Edlington formation between them, though in the Durham area this last is replaced by the Fordham Evaporite Formation and

2028-399: The only genus of cephalopod that has a well-developed external shell. Females of the cephalopod genus Argonauta create a papery egg case which sometimes washes up on tropical beaches and is referred to as a "paper nautilus". The largest group of shelled cephalopods, the ammonites , are extinct, but their shells are very common in certain areas as fossils . Empty molluscan seashells are

2080-455: The only kind of shells; in various habitats, there are shells from freshwater animals such as freshwater mussels and freshwater snails , and shells of land snails . When the word "seashells" refers only to the shells of marine mollusks, then studying seashells is part of conchology . Conchologists or serious collectors who have a scientific bias are in general careful not to disturb living populations and habitats: even though they may collect

2132-695: The planet, there are far more species of colorful, large, shallow water shelled marine mollusks than there are in the temperate zones and the regions closer to the poles. Although there are a number of species of shelled mollusks that are quite large, there are vast numbers of extremely small species too, see micromollusks . Not all mollusks are marine. There are numerous land and freshwater mollusks, see for example snail and freshwater bivalves . In addition, not all mollusks have an external shell: some mollusks such as some cephalopods (squid and octopuses) have an internal shell, and many mollusks have no shell, see for example slug and nudibranch . Bivalves are often

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2184-647: The production of lime . Along the Gulf Coast of the United States , oyster shells were mixed into cement to make "shellcrete" which could form bricks, blocks and platforms. It could also be applied over logs. A notable example is the 19th-century Sabine Pass Lighthouse in Louisiana, near Texas. Many arthropods have sclerites , or hardened body parts, which form a stiff exoskeleton made up mostly of chitin . In crustaceans , especially those of

2236-485: The ruins of Rome, though they are thought to have been brought from Magnesia in Greece. Carbonate rock Carbonate rocks are also crucial components to understanding geologic history due to processes such as diagenesis in which carbonates undergo compositional changes based on kinetic effects . The correlation between this compositional change and temperature can be exploited to reconstruct past climate as

2288-571: The same purpose (and more). The changes in trace metal ratios from carbonate minerals found here can be used to determine patterns from parent [carbonate] rocks, too. Seashell A seashell or sea shell , also known simply as a shell , is a hard, protective outer layer usually created by an animal or organism that lives in the sea. Most seashells are made by mollusks , such as snails , clams , and oysters to protect their soft insides. Empty seashells are often found washed up on beaches by beachcombers . The shells are empty because

2340-512: The seafloor is calcite, while aragonite is more found in biological organisms. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature , pH , and dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement

2392-549: The shell or cutting off the tip of the spire altogether. Various different kinds of large marine gastropod shells can be turned into "blowing shells"; however, the most commonly encountered species used as " conch " trumpets are: Children in some cultures are often told the myth that you can hear the sound of the ocean by holding a seashell to ones ear. This is due to the effect of seashell resonance . Whole seashells or parts of sea shells have been used as jewelry or in other forms of adornment since prehistoric times. Mother of pearl

2444-446: The shells were collected. On the other hand, some collectors buy the more widely available commercially imported exotic shells, the majority of which have very little data, or none at all. To museum scientists, having full collecting data (when, where, and by whom it was collected) with a specimen is far more important than having the shell correctly identified. Some owners of shell collections hope to be able to donate their collection to

2496-570: The species level can be very difficult, because of the great variability within many species and families. The identification of certain individual species is often very difficult, even for a specialist in that particular family. Some species cannot be differentiated on the basis of shell character alone. Numerous smaller and more obscure mollusk species (see micromollusk ) are yet to be discovered and named. In other words, they have not yet been differentiated from similar species and assigned scientific (binomial) names in articles in journals recognized by

2548-404: The time of growth. Diagenesis refers to the process whereby sediments are being converted to sedimentary rock. This includes biological activity, erosion, and other chemical reactions. Due to the strong correlation between diagenesis and seawater temperature , coral skeletons can be used as proxies for understanding past climate effects. Specifically, the ratio of Strontium to Calcium in

2600-603: The world as food and as a source of pearls. The larvae of some freshwater mussels can be dangerous to fish and can bore through wood. Shell Beach, Western Australia , is a beach which is entirely made up of the shells of the cockle Fragum erugatum . Certain species of gastropod seashells (the shells of sea snails ) can sometimes be common, washed up on sandy beaches, and also on beaches that are surrounded by rocky marine habitat. Chiton plates or valves often wash up on beaches in rocky areas where chitons are common. Chiton shells, which are composed of eight separate plates and

2652-528: Was first published in 1791 and has been found across the Earth's crust from various different time periods . Because the rock is made of calcium , magnesium , and carbonate ions, the mineral crystalline structure can be visualized similar to calcite and magnesite . Due to this composition, the dolomite mineral present in dolostone can be classified by varying degree of calcium inclusion, and occasionally iron, too. Calcium-rich dolomite, or calcian dolomite,

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2704-486: Was historically primarily a seashell product, although more recently some mother of pearl comes from freshwater mussels. Also see pearl . " Sailor's Valentines " were late 19th-century decorative keepsakes which were made from the Caribbean, and which were often purchased by sailors to give to their loved ones back home for example in England. These valentines consisted of elaborate arrangements of small seashells glued into attractive symmetrical designs, which were encased on

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