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63-629: Due to the prominent rocks ( sponge reefs in cone karst shapes ) of a meander cutoff hill, which emerged as the result of the uplifting of the Franconian Jura in the Late Tertiary and the deposition of a thick bed of sand in the Upper Cretaceous, and its timber-framed-houses, which appear in places to be glued onto the rocks, Tüchersfeld is a symbol of Franconian Switzerland and has also been portrayed on postage stamps of

126-532: A discontinuous reef system 7,000 km long stretched across the northern Tethys and North Atlantic basins. This chain of sponge reefs is the largest known biostructure to have ever existed on Earth. The sponge reefs declined throughout the Cretaceous period as coral and rudist reefs were becoming prominent. It is theorized that the spread of diatoms may have been detrimental to the sponges, as diatoms compete with hexactinellid sponges for silica. It

189-407: A glass with no true melting point, can be used as a glass fibre for fibreglass. Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz . Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product. Precipitated silica or amorphous silica is produced by

252-494: A heat capacity minimum. Its density decreases from 2.08 g/cm at 1950 °C to 2.03 g/cm at 2200 °C. The molecular SiO 2 has a linear structure like CO 2 . It has been produced by combining silicon monoxide (SiO) with oxygen in an argon matrix. The dimeric silicon dioxide, (SiO 2 ) 2 has been obtained by reacting O 2 with matrix isolated dimeric silicon monoxide, (Si 2 O 2 ). In dimeric silicon dioxide there are two oxygen atoms bridging between

315-450: A low value of 140° in α-tridymite, up to 180° in β-tridymite. In α-quartz, the Si–O–Si angle is 144°. Alpha quartz is the most stable form of solid SiO 2 at room temperature. The high-temperature minerals, cristobalite and tridymite, have both lower densities and indices of refraction than quartz. The transformation from α-quartz to beta-quartz takes place abruptly at 573 °C. Since

378-410: A silicon wafer enables it to overcome the surface states that otherwise prevent electricity from reaching the semiconducting layer. The process of silicon surface passivation by thermal oxidation (silicon dioxide) is critical to the semiconductor industry . It is commonly used to manufacture metal–oxide–semiconductor field-effect transistors (MOSFETs) and silicon integrated circuit chips (with

441-482: A substrate. Without a hard substrate, new sponges cannot settle and regrow broken parts of the reef. It has been estimated that broken sponge reefs may take up to 200 years to recover. In addition, offshore oil and gas exploration threatens the reefs. The government of British Columbia has lifted a moratorium preventing exploratory drilling and tanker traffic in Hecate Strait and Queen Charlotte Sound, and

504-477: A very shallow layer of about 1 nm or 10 Å of so-called native oxide. Higher temperatures and alternative environments are used to grow well-controlled layers of silicon dioxide on silicon, for example at temperatures between 600 and 1200 °C, using so-called dry oxidation with O 2 or wet oxidation with H 2 O. The native oxide layer is beneficial in microelectronics , where it acts as electric insulator with high chemical stability. It can protect

567-524: A white powder with extremely low bulk density (0.03-0.15 g/cm ) and thus high surface area. The particles act as a thixotropic thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications. Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without

630-685: A white robe as he turns to people of different ages. On the side altar is a painting by Anna Maria, Baroness of Oer (Gößweinstein) which shows the Madonna and Child . The ceiling murals, included one of the Lamb of God and the Four Evangelists . The statues in the gallery and the Stations of the Cross are sculpted by Giovanni Bruno (Gößweinstein). On 1 January 1972, the municipality of Tüchersfeld

693-439: Is also the primary component of rice husk ash , which is used, for example, in filtration and as supplementary cementitious material (SCM) in cement and concrete manufacturing. Silicification in and by cells has been common in the biological world and it occurs in bacteria, protists, plants, and animals (invertebrates and vertebrates). Prominent examples include: About 95% of the commercial use of silicon dioxide (sand)

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756-399: Is an oxide of silicon with the chemical formula SiO 2 , commonly found in nature as quartz . In many parts of the world, silica is the major constituent of sand . Silica is one of the most complex and abundant families of materials , existing as a compound of several minerals and as a synthetic product. Examples include fused quartz , fumed silica , opal , and aerogels . It

819-604: Is covalently bonded in a tetrahedral manner to 4 oxygen atoms. In contrast, CO 2 is a linear molecule. The starkly different structures of the dioxides of carbon and silicon are a manifestation of the double bond rule . Based on the crystal structural differences, silicon dioxide can be divided into two categories: crystalline and non-crystalline (amorphous). In crystalline form, this substance can be found naturally occurring as quartz , tridymite (high-temperature form), cristobalite (high-temperature form), stishovite (high-pressure form), and coesite (high-pressure form). On

882-399: Is estimated through radiocarbon dating of reef cores that the reefs have been living on the continental shelf of Western Canada for 8,500–9,000 years. Sponge reefs provide structure on the otherwise relatively featureless continental shelf. They provide habitat for fish and invertebrates, and may serve as an important nursery area for these animals. More research is required to determine

945-465: Is in the construction industry, e.g. in the production of concrete ( Portland cement concrete ). Certain deposits of silica sand, with desirable particle size and shape and desirable clay and other mineral content, were important for sand casting of metallic products. The high melting point of silica enables it to be used in such applications such as iron casting; modern sand casting sometimes uses other minerals for other reasons. Crystalline silica

1008-651: Is obtained by the dealumination of a low-sodium, ultra-stable Y zeolite with combined acid and thermal treatment. The resulting product contains over 99% silica, and has high crystallinity and specific surface area (over 800 m /g). Faujasite-silica has very high thermal and acid stability. For example, it maintains a high degree of long-range molecular order or crystallinity even after boiling in concentrated hydrochloric acid . Molten silica exhibits several peculiar physical characteristics that are similar to those observed in liquid water : negative temperature expansion, density maximum at temperatures ~5000 °C, and

1071-421: Is rapidly cooled, it does not crystallize, but solidifies as a glass. Because of this, most ceramic glazes have silica as the main ingredient. The structural geometry of silicon and oxygen in glass is similar to that in quartz and most other crystalline forms of silicon and oxygen, with silicon surrounded by regular tetrahedra of oxygen centres. The difference between the glass and crystalline forms arises from

1134-409: Is stable and consists of rock, coarse gravel, and large boulders. Hexactinellid sponges require a hard substrate, and do not anchor to muddy or sandy sea floors. They are found only where sedimentation rates are low, dissolved silica is high (43–75 μM), and bottom currents are between 0.15 and 0.30 m/s. Dissolved oxygen is low (64–152 μM), and temperatures are a cool 5.5-7.3 °C at

1197-405: Is that their tissues are made up almost entirely of syncytia. In a syncytium there are many nuclei in a continuous cytoplasm; nuclei are not packaged in discrete cells. As a result, the sponge has a distinctive electrical conduction system across its body. This allows the sponge to rapidly respond to disturbances such as a physical impact or excessive sediment in the water. The sponge's response

1260-571: Is the synagogue from the second half of the 18th century (around 1763) with its simple Late Baroque stucco work on the ceiling; of the original decoration little can be seen after decades of alienation. The Catholic chapel of ease , the Church of the Sacred Heart, was built in 1950-51 thanks to a foundation; with the tower it is attached to another building. Behind the altar is a painting by Otelia Kraszewska (Gößweinstein) depicting Christ in

1323-426: Is the major constituent of sand . Even though it is poorly soluble, silica occurs in many plants such as rice . Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates . Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation. Silica

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1386-457: Is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms coesite and stishovite have been found around impact structures and associated with eclogites formed during ultra-high-pressure metamorphism . The high-temperature forms of tridymite and cristobalite are known from silica-rich volcanic rocks . In many parts of the world, silica

1449-504: Is the process by which a semiconductor surface is rendered inert, and does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal. The formation of a thermally grown silicon dioxide layer greatly reduces the concentration of electronic states at the silicon surface . SiO 2 films preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by

1512-419: Is to stop feeding. It will try to resume feeding after 20–30 minutes, but will stop again if the irritation is still present. Hexactinellids are exclusively marine and are found throughout the world in deep (>1000 m) oceans. Individual sponges grow at a rate of 0–7 cm/year, and can live to be at least 220 years old. Little is known about hexactinellid sponge reproduction. Like all poriferans,

1575-436: Is used as a fining agent for wine, beer, and juice, with the E number reference E551 . In cosmetics, silica is useful for its light-diffusing properties and natural absorbency. Diatomaceous earth , a mined product, has been used in food and cosmetics for centuries. It consists of the silica shells of microscopic diatoms ; in a less processed form it was sold as "tooth powder". Manufactured or mined hydrated silica

1638-489: Is used as the hard abrasive in toothpaste . Silicon dioxide is widely used in the semiconductor technology: Because silicon dioxide is a native oxide of silicon it is more widely used compared to other semiconductors like gallium arsenide or indium phosphide . Silicon dioxide could be grown on a silicon semiconductor surface. Silicon oxide layers could protect silicon surfaces during diffusion processes , and could be used for diffusion masking. Surface passivation

1701-418: Is used in hydraulic fracturing of formations which contain tight oil and shale gas . Silica is the primary ingredient in the production of most glass . As other minerals are melted with silica, the principle of freezing point depression lowers the melting point of the mixture and increases fluidity. The glass transition temperature of pure SiO 2 is about 1475 K. When molten silicon dioxide SiO 2

1764-498: Is used in structural materials , microelectronics , and as components in the food and pharmaceutical industries. All forms are white or colorless, although impure samples can be colored. Silicon dioxide is a common fundamental constituent of glass . In the majority of silicon dioxides, the silicon atom shows tetrahedral coordination , with four oxygen atoms surrounding a central Si atom ( see 3-D Unit Cell ). Thus, SiO 2 forms 3-dimensional network solids in which each silicon atom

1827-538: Is used to produce elemental silicon . The process involves carbothermic reduction in an electric arc furnace : Fumed silica , also known as pyrogenic silica, is prepared by burning SiCl 4 in an oxygen-rich hydrogen flame to produce a "smoke" of SiO 2 . It can also be produced by vaporizing quartz sand in a 3000 °C electric arc. Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles,

1890-717: The Deutsche Post . Until the Thirty Years' War there were two castles here, the Upper and Lower Castles , the latter was recorded in 1269 as a fortress that had already been in existence for a long time. The Franconian Switzerland Museum is housed in the old Judenhof ("Jews Court"), a group of 17th- and 18th-century buildings built by Jews on the grounds of the Lower Castle and inhabited until 1860 by 18 Jewish families, and restored in 1978–1982. Of particular note

1953-603: The North Coast of British Columbia were consolidated within the Pacific North Coast Integrated Management Area . The goal was to develop a plan to conserve this relatively undeveloped region, while fostering sustainable economies on the coast, which promised to make Canada a world leader in marine conservation. However, in 2011, the ministry withdrew support for the process in favour of greater consistency with ocean planning on

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2016-555: The planar process ). Hydrophobic silica is used as a defoamer component . In its capacity as a refractory , it is useful in fiber form as a high-temperature thermal protection fabric. Silica is used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes . Silica aerogel was used in the Stardust spacecraft to collect extraterrestrial particles. Pure silica (silicon dioxide), when cooled as fused quartz into

2079-611: The strait of Georgia and Howe sound close to Vancouver . Although still common in the late Jurassic period, reef-building sponges were believed to have gone extinct during or shortly after the Cretaceous period , until the existing reefs were discovered in Queen Charlotte sound in 1987–1988 – hence these sometimes being dubbed living fossils . Like coral reefs , sponge reefs serve an important ecological function as feeding, breeding and nursery habitats for demersal fish and invertebrates but are currently threatened by

2142-569: The Queen Charlotte Basin (QCB) in 1987–1988. Three more reefs were reported in the Georgia Basin (GB) in 2005. The QCB reefs are found 70–80 km from the coastline in water 165–240 m deep. These reefs cover over 700 km² of the ocean floor. Sponge reefs require unique conditions, which may explain their global rarity. They are found only in glacier-scoured troughs of low-angle continental shelf . The seafloor

2205-496: The acidification of solutions of sodium silicate . The gelatinous precipitate or silica gel , is first washed and then dehydrated to produce colorless microporous silica. The idealized equation involving a trisilicate and sulfuric acid is: Approximately one billion kilograms/year (1999) of silica were produced in this manner, mainly for use for polymer composites – tires and shoe soles. Thin films of silica grow spontaneously on silicon wafers via thermal oxidation , producing

2268-519: The adult sponge that firmly anchors the animal to the reef. Deep ocean currents carry fine sediments that are captured by the scaffolding of sponge reefs. A sediment matrix of silt, clay, and some sand forms around the base of the sponge bioherms. The sediment matrix is soft near the surface, and firm below one metre deep. Dead sponges become covered in sediment, but do not lose their supportive siliceous skeleton. The sponge sediments have high levels of silica and organic carbon. The reefs grow parallel to

2331-445: The area has been leased by the oil and gas industry. Even if exploratory drilling is not done on or immediately adjacent to the reefs, it may still have a negative impact by increasing the amount of sediment in the seawater, or through hydrocarbon pollution. In 1999, Fisheries and Oceans Canada requested that groundfish trawlers voluntarily avoid the sponge reefs. In 2002, following reports of new reef damage sustained since 1999,

2394-552: The branching of the pyrogenic product. The main use is as pozzolanic material for high performance concrete. Fumed silica nanoparticles can be successfully used as an anti-aging agent in asphalt binders. Silica, either colloidal, precipitated, or pyrogenic fumed, is a common additive in food production. It is used primarily as a flow or anti- caking agent in powdered foods such as spices and non-dairy coffee creamer, or powders to be formed into pharmaceutical tablets. It can adsorb water in hygroscopic applications. Colloidal silica

2457-463: The commercial fishery, offshore oil and gas industries. Attempts are being made to protect these unique ecosystems through fishery closures and potentially the establishment of Marine Protected Areas (MPAs) around the sponge reefs. Hexactinellids, or "glassy" sponges are characterized by a rigid framework of spicules made of silica . Unlike other poriferans, hexactinellids do not possess the ability to contract. Another unique feature of glassy sponges

2520-509: The connectivity of the tetrahedral units: Although there is no long-range periodicity in the glassy network, ordering remains at length scales well beyond the SiO bond length. One example of this ordering is the preference to form rings of 6-tetrahedra. The majority of optical fibers for telecommunications are also made from silica. It is a primary raw material for many ceramics such as earthenware , stoneware , and porcelain . Silicon dioxide

2583-495: The death of the sponge. Other sponge species abundant on sponge reefs are members of the order Lyssactinosa (Rosselid sponges) and include Rhabdocalyptus dawsoni (boot sponge), Acanthascus platei , Acanthascus cactus and Staurocalyptus dowlingi . Rosselid sponges have a "woven" or "loose" siliceous skeleton that does not persist after the death of the sponge, and are capable of forming mats, but not reefs. Although hexactinellid sponges are found worldwide in deep seawater,

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2646-488: The densest of the low-pressure forms, which has a density of 2.648 g/cm . The difference in density can be ascribed to the increase in coordination as the six shortest Si–O bond lengths in stishovite (four Si–O bond lengths of 176 pm and two others of 181 pm) are greater than the Si–O bond length (161 pm) in α-quartz. The change in the coordination increases the ionicity of the Si–O bond. Faujasite silica, another polymorph,

2709-624: The full ecological importance of these reefs. Observations by crewed submersible indicate that the fauna of sponge reefs differs from surrounding areas. Organisms found in and around sponge reefs include annelid worms, bryozoans , spider crab, King crab, shrimp, prawns, and euphausids . Echinoderms , especially sea urchins and sea stars, were abundant in areas of the reef where the sponges were dying or deceased, and can be used as an indicator of sponge reef health. Rockfish, especially Sebastes species, live in openings and in between sponges. Gravid and juvenile rockfish were observed, suggesting that

2772-411: The gaseous ambient environment. Silicon oxide layers could be used to electrically stabilize silicon surfaces. The surface passivation process is an important method of semiconductor device fabrication that involves coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. Growing a layer of silicon dioxide on top of

2835-626: The glacial troughs, and the morphology of reefs is due to deep currents. Hexactinellids first appeared in the fossil record during the Late Proterozoic , and the first hexactinosans were found in the Late Devonian . Hexactinellid sponge reefs were first identified in the Middle Triassic (245-208 million years ago). The sponges reached their full extent in the late Jurassic (201-145 million years ago) when

2898-515: The hexactinellids are filter feeders. They obtain nutrition from direct absorption of dissolved substances, and to a lesser extent from particulate materials. There are no known predators of healthy reef sponges. This is likely because the sponges possess very little organic tissue; the siliceous skeleton accounts for 90% of the sponge body weight. Hexasterophoran sponges have spicules called hexactines that have six rays set at right angles. Orders within hexasterophora are classified by how tightly

2961-428: The ministry initiated regulated closures of groundfish trawling and voluntary closures of shrimp trawl fishing in areas where sponge reefs were known to inhabit. Protection of the four sponge reefs in Hecate Strait and Queen Charlotte Sound was included as a "management issue" in the 2005/06 groundfish trawling management plan. The management plan recommended that an additional 9 km (5.6 mi) buffer zone around

3024-484: The non-spiculed, calcite -skeletoned archaeocyathid and stromatoporoid sponges were the primary reef-builders. Sponge reefs were once a dominant landscape in the Paleozoic and Mesozoic sea, but are now very rare, and found only in waters off the coast of North America 's Pacific Northwest region, more specifically southern Alaska , British Columbia and Washington . Sponge reefs were reported in 2018 within

3087-644: The only place that they are known to form reefs is between south east Alaska and off Grays harbor . Communities of Rosselid sponges called "sponge mats" are widely distributed; they are found in canyons in the North Atlantic, in the Canadian Arctic and on Antarctic continental shelves. There is also a reef formed of siliceous Demospongiae species off of Axel Heiberg Island in the Arctic Ocean. Four hexactinellid reefs were discovered in

3150-413: The order Hexactinosa has a rigid skeleton that persists after the death of the animal. This provides an excellent substrate for sponge larvae to settle upon, and new sponges grow on the framework of past generations. The growth of sponge reefs is thus analogous to that of coral reefs . The tendrils of new sponges wrap around spicules of older, deceased sponges. The tendrils will later form the basal plate of

3213-513: The other coasts of Canada. In February 2017, the sponge reefs of Hecate Sound and Queen Charlotte Sound were formally protected within the Hecate Strait and Queen Charlotte Sound Glass Sponge Reefs Marine Protected Area . The marine protected area covers an area of 2,410 km (930 sq mi) and prohibits any activity that could disturb or destroy the sponge reefs. Silica Silicon dioxide , also known as silica ,

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3276-400: The other hand, amorphous silica can be found in nature as opal and diatomaceous earth . Quartz glass is a form of intermediate state between these structures. All of these distinct crystalline forms always have the same local structure around Si and O. In α-quartz the Si–O bond length is 161 pm, whereas in α-tridymite it is in the range 154–171 pm. The Si–O–Si angle also varies between

3339-545: The reefs are being used as a nursery area. Foraminiferans are abundant around the reefs, and diatoms are scarce. The consortium of organisms living in and around sponge reefs has changed very little since the Jurassic. The reefs are susceptible to damage by fishing, especially bottom trawling and dredging. In typical groundfish trawling, a large net is dragged across the ocean floor, its mouth held open by two 2 tonne doors called otterboards. The siliceous skeleton of

3402-400: The reefs be added to the existing groudfish trawl closures. The reefs were also being considered as locations for future Marine Protected Areas (MPAs). Although MPAs may be more effective than fishery closures for long-term protection of the reefs from bottom trawling, the oil and gas industry would still pose a threat. In 2008, the issue of preserving sensitive underwater ecosystems along

3465-674: The reefs. Surface temperatures range between 6 °C in April and 14 °C in August. Downwellings are common in Hecate Strait and Queen Charlotte Sound , especially in winter, but there is an occasional summer upwelling . These upwellings bring nutrient-rich waters to the sponge reefs. Each living sponge on the surface of the reef can be over 1.5 m tall. The reefs are composed of mounds called "bioherms" that are up to 21 m high, and sheets called "biostromes" that are 2–10 m thick and may be many kilometers wide. Each sponge in

3528-443: The reefs. When the fishing gear is hauled to the surface, the lines and traps drag along the ocean floor and have the potential to break corals and sponges. Broken sponge "stumps", as well as those with abraded sides, were found in regions where line and trap fishing took place. Breakage of reef sponges may have dire consequences for the recruitment of new sponges, as sponge larvae require the siliceous skeletons of past generations as

3591-401: The silicon atoms with an Si–O–Si angle of 94° and bond length of 164.6 pm and the terminal Si–O bond length is 150.2 pm. The Si–O bond length is 148.3 pm, which compares with the length of 161 pm in α-quartz. The bond energy is estimated at 621.7 kJ/mol. SiO 2 is most commonly encountered in nature as quartz , which comprises more than 10% by mass of the Earth's crust. Quartz

3654-418: The silicon, store charge, block current, and even act as a controlled pathway to limit current flow. Many routes to silicon dioxide start with an organosilicon compound, e.g., HMDSO, TEOS. Synthesis of silica is illustrated below using tetraethyl orthosilicate (TEOS). Simply heating TEOS at 680–730 °C results in the oxide: Similarly TEOS combusts around 400 °C: TEOS undergoes hydrolysis via

3717-492: The so-called sol-gel process . The course of the reaction and nature of the product are affected by catalysts, but the idealized equation is: Being highly stable, silicon dioxide arises from many methods. Conceptually simple, but of little practical value, combustion of silane gives silicon dioxide. This reaction is analogous to the combustion of methane: However the chemical vapor deposition of silicon dioxide onto crystal surface from silane had been used using nitrogen as

3780-412: The spicules interlock with Lyssanctinosan spicules less tightly interlocked than those of Hexactinosan sponges. The primary frame-building sponges are all members of the order Hexactinosa, and include the species Chonelasma/Heterochone calyx (chalice sponge), Aphrocallistes vastus ( cloud sponge ), and Farrea occa . Hexactinosan sponges have a rigid scaffolding of "fused" spicules that persists after

3843-575: The sponges is fragile, and these organisms are easily broken by physical impact. The impacts of bottom trawling have been observed in three of the reefs in the QCB. Trawling damage appears as parallel tracks 70–100 m apart that may extend for several kilometers. Each trawl track is 10 cm deep, 20 cm wide, and occurs at depths of 210–220 m. Sponges in the vicinity of trawl tracks are shattered or completely removed. While less harmful, hook and line fishing as well as crustacean trapping may also damage

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3906-446: The transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit. The high-pressure minerals, seifertite , stishovite, and coesite, though, have higher densities and indices of refraction than quartz. Stishovite has a rutile -like structure where silicon is 6-coordinate. The density of stishovite is 4.287 g/cm , which compares to α-quartz,

3969-405: Was dissolved and its territory was incorporated into the boroughs of Pottenstein and Gößweinstein (the hamlets of Hühnerloh and Kohlenstein). Sponge reef Sponge reefs are reefs produced by sea sponges . All modern sponge reefs are formed by hexactinellid sponges, which have an endoskeleton made of silica spicules and are often referred to as "glass sponges", while historically

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