The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk . Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites , and the living nautiluses , cuttlefish , and Spirula . In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the septa (walls) dividing the camerae (chambers). Some older studies have used the term siphon for the siphuncle, though this naming convention is uncommon in modern studies to prevent confusion with a mollusc organ of the same name .
50-804: The Tarphyceratidae are tightly coiled, evolute Tarphycerida with ventral siphuncles . The dorsum is characteristically impressed where the whorl presses against the venter of the previous. The Tarphyceratidae are derived from Bassleroceras or possibly from some member of the Estonioceratidae . Tarphyceratids vary in form and siphuncle position. The siphuncle may be subcentral as in Centrotarphyceras ; intermediary as in Tarphyceras , or subventral as in Campbelloceras . Cross sections vary. Tarphyceras and Campbelloceras are rounded. Centrotarphyceras
100-436: A dissolution and reprecipitation mechanism, with the reaction rate controlled by the surface area of a calcite crystal. The second stage of the reaction is approximately 10 times slower. However, crystallization of calcite has been observed to be dependent on the starting pH and concentration of magnesium in solution. A neutral starting pH during mixing promotes the direct transformation of ACC into calcite without
150-531: A goniometer , and looking for the smallest numbers that fit. Later, a "structural" unit cell was determined using X-ray crystallography . The morphological unit cell is rhombohedral , having approximate dimensions a = 10 Å and c = 8.5 Å , while the structural unit cell is hexagonal (i.e. a rhombic prism ), having approximate dimensions a = 5 Å and c = 17 Å . For the same orientation, c must be multiplied by 4 to convert from morphological to structural units. As an example, calcite cleavage
200-527: A specific gravity of 2.71 and, in crystalline varieties, a vitreous luster . Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities. Calcite has numerous habits, representing combinations of over 1000 crystallographic forms . Most common are scalenohedra , with faces in the hexagonal {2 1 1} directions (morphological unit cell) or {2 1 4} directions (structural unit cell); and rhombohedral, with faces in
250-607: A clear piece of calcite to appear doubled. The birefringent effect (using calcite) was first described by the Danish scientist Rasmus Bartholin in 1669. At a wavelength of about 590 nm, calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the ordinary refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite has thermoluminescent properties mainly due to manganese divalent ( Mn ). An experiment
300-399: A higher rate of metabolic activity. The siphuncle of fossilised cephalopods is assumed to have worked in the same general way as in living nautiluses . The siphuncle itself is only rarely preserved, but its shape can be inferred from hardened structures which lie around it. Many fossils show the holes where the siphuncle passes through each septum. Around these holes, the rim of the septum
350-405: A monohydrocalcite intermediate, sequestering carbon . Calcite is often the primary constituent of the shells of marine organisms , such as plankton (such as coccoliths and planktic foraminifera ), the hard parts of red algae , some sponges , brachiopods , echinoderms , some serpulids , most bryozoa , and parts of the shells of some bivalves (such as oysters and rudists ). Calcite
400-402: A stable buoyancy with minimal effort. In the geologic past, many cephalopods grew to an enormous size (perhaps approaching ten meters in length) thanks to this. Generally, the siphuncle is unable to provide a way to change the density of shell rapidly and thus cause the animal to rise or sink at will; rather, the animal must swim up or down as required. Cephalopods with a wider siphuncle have
450-526: A vaterite intermediate. But when ACC forms in a solution with a basic initial pH, the transformation to calcite occurs via metastable vaterite, following the pathway outlined above. Magnesium has a noteworthy effect on both the stability of ACC and its transformation to crystalline CaCO 3 , resulting in the formation of calcite directly from ACC, as this ion destabilizes the structure of vaterite. Epitaxial overgrowths of calcite precipitated on weathered cleavage surfaces have morphologies that vary with
500-543: Is a very common mineral, particularly as a component of limestone . Calcite defines hardness 3 on the Mohs scale of mineral hardness , based on scratch hardness comparison . Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite . Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, and vaterite
550-400: Is bent into a stout aragonitic tube known as a septal neck (or siphuncle notch). In each chamber of the shell, the siphuncle is encased by a tubular structure known as a connecting ring . In living nautiluses, the connecting ring is a simple, thin-walled cylinder, with organic or thinly calcitic layers secreted from the tissues of the siphuncle. This fragile and poorly-mineralized form
SECTION 10
#1732877037528600-441: Is designed to promote sustainable development in the mining industry. Calcite can help synthesize precipitated calcium carbonate (PCC) (mainly used in the paper industry) and increase carbonation . Furthermore, due to its particular crystal habit, such as rhombohedron, hexagonal prism, etc., it promotes the production of PCC with specific shapes and particle sizes. Calcite, obtained from an 80 kg sample of Carrara marble ,
650-437: 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 that of dolomite , MgCa(CO 3 ) 2 . Calcite can also contain small quantities of iron and manganese . Manganese may be responsible for the fluorescence of impure calcite, as may traces of organic compounds. Calcite
700-514: Is even less stable. Calcite is derived from the German Calcit , a term from the 19th century that came from the Latin word for lime , calx (genitive calcis ) with the suffix -ite used to name minerals. It is thus a doublet of the word chalk . When applied by archaeologists and stone trade professionals, the term alabaster is used not just as in geology and mineralogy, where it
750-741: Is found all over the world, and its leading global distribution is as follows: Calcite is found in many different areas in the United States. One of the best examples is the Calcite Quarry in Michigan. The Calcite Quarry is the largest carbonate mine in the world and has been in use for more than 85 years. Large quantities of calcite can be mined from these sizeable open pit mines. Calcite can also be found throughout Canada, such as in Thorold Quarry and Madawaska Mine, Ontario, Canada. Abundant calcite
800-459: Is found in spectacular form in the Snowy River Cave of New Mexico as mentioned above, where microorganisms are credited with natural formations. Trilobites , which became extinct a quarter billion years ago , had unique compound eyes that used clear calcite crystals to form the lenses. It also forms a substantial part of birds' eggshells, and the δ C of the diet is reflected in the δ C of
850-407: Is given as "perfect on {1 0 1 1}" in morphological coordinates and "perfect on {1 0 1 4}" in structural units. In { h k l } {\displaystyle \{hkl\}} indices, these are {1 0 1} and {1 0 4}, respectively. Twinning , cleavage and crystal forms are often given in morphological units. The diagnostic properties of calcite include a defining Mohs hardness of 3,
900-425: Is known as a nautilosiphonate morphology. Many extinct cephalopods have a much more prominent connecting ring, with a very thick and porous inner calcitic layer. This more strongly-mineralized form is known as a calciosiphonate connecting ring. Connecting rings are strongly variable in morphology, from narrow homogenous tubes to bulbous, segmented cavities. Some are infolded, sending lobes or blades of calcite into
950-757: Is mined in the Santa Eulalia mining district, Chihuahua, Mexico. Large quantities of calcite in Iceland are concentrated in the Helgustadir mine . The mine was once the primary mining location of "Iceland spar." However, it currently serves as a nature reserve, and calcite mining will not be allowed. Calcite is found in parts of England, such as Alston Moor, Egremont, and Frizington, Cumbria. St. Andreasberg, Harz Mountains, and Freiberg, Saxony can find calcite. Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast , whose name contributed to
1000-444: Is not a form of active pumping: the gas moving into the chamber is a passive process. Most energy is expended through the absorption of water from the chamber. Removing water from the chambers of the shell reduces the overall density of the shell, and thus the shell behaves as a flotation device comparable to the swim bladder in bony fish . Typically, cephalopods maintain a density close to that of sea water , allowing them to keep
1050-554: Is one of the minerals that has been shown to catalyze an important biological reaction, the formose reaction , and may have had a role in the origin of life. Interaction of its chiral surfaces (see Form ) with aspartic acid molecules results in a slight bias in chirality; this is one possible mechanism for the origin of homochirality in living cells. Climate change is exacerbating ocean acidification , possibly leading to lower natural calcite production. The oceans absorb large amounts of CO 2 from fossil fuel emissions into
SECTION 20
#17328770375281100-501: Is reserved for a variety of gypsum ; but also for a similar-looking, translucent variety of fine-grained banded deposit of calcite. In publications, two different sets of Miller indices are used to describe directions in hexagonal and rhombohedral crystals, including calcite crystals: three Miller indices h, k, l in the a 1 , a 2 , c {\displaystyle a_{1},a_{2},c} directions, or four Bravais–Miller indices h, k, i, l in
1150-556: Is subquadrate with broadly rounded flanks and a slightly rounded venter. Eurystomites is subquadrate and slightly compressed, with the maximum width closer to the dorsum. Pionoceras is subrounded and slightly depressed with the maximum width closer to the venter. The dorsal impression in Tarphyceras and Eurystomites is broad and deep and in Pionoceras and Centrotarphyceras , broad and shallow. In Campbelloceras and Cycloplectoceras
1200-403: Is the leading cause of excessive growth of cyanobacteria. As an active capping material, calcite can help reduce P release from sediments into the water, thus inhibiting cyanobacteria overgrowth. Calcite is a common constituent of sedimentary rocks , limestone in particular, much of which is formed from the shells of dead marine organisms. Approximately 10% of sedimentary rock is limestone. It
1250-474: Is the primary mineral in metamorphic marble . It also occurs in deposits from hot springs as a vein mineral; in caverns as stalactites and stalagmites ; and in volcanic or mantle-derived rocks such as carbonatites , kimberlites , or rarely in peridotites . Cacti contain Ca-oxalate biominerals. Their death releases these biominerals into the environment, which subsequently transform to calcite via
1300-586: Is used as the IAEA -603 isotopic standard in mass spectrometry for the calibration of δ O and δ C . Calcite can be formed naturally or synthesized. However, artificial calcite is the preferred material to be used as a scaffold in bone tissue engineering due to its controllable and repeatable properties. Calcite can be used to alleviate water pollution caused by the excessive growth of cyanobacteria . Lakes and rivers can lead to cyanobacteria blooms due to eutrophication , which pollutes water resources. Phosphorus (P)
1350-524: Is used for optical purposes. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the rhombohedral form is sometimes referred to as "nailhead spar". The rhombohedral form may also have been the " sunstone " whose use by Viking navigators is mentioned in the Icelandic Sagas . Single calcite crystals display an optical property called birefringence (double refraction). This strong birefringence causes objects viewed through
1400-399: Is used primarily in emptying water from new chambers as the shell grows. To perform this task, the cephalopod increases the saltiness of the blood in the siphuncle, and the water moves from the more dilute chamber into the blood through osmosis . At the same time gasses, mostly nitrogen , oxygen , and carbon dioxide , diffuse from the blood in the siphuncle into the emptying chamber. This
1450-471: The a 1 , a 2 , a 3 , c {\displaystyle a_{1},a_{2},a_{3},c} directions, where i {\displaystyle i} is redundant but useful in visualizing permutation symmetries . To add to the complications, there are also two definitions of unit cell for calcite. One, an older "morphological" unit cell, was inferred by measuring angles between faces of crystals, typically with
1500-629: The Lower Ordovician in North America. For purposes of discussion only, they are divided into those where dorsum, which is on the inside or concave side of the volutions, is more deeply impressed and those with dorsum that is only moderately or slightly impressed. (Fig 262,K359,Furnish and Glenister, 1964) Tarphyceratidae with dorsum deeply impressed Tarphycerida with dorsum slightly to moderately impressed Uncertain Siphuncle The siphuncle
1550-690: The calcite of the shell. The largest documented single crystal of calcite originated from Iceland, measured 7 m × 7 m × 2 m (23 ft × 23 ft × 6.6 ft) and 6 m × 6 m × 3 m (20 ft × 20 ft × 9.8 ft) and weighed about 250 tons. Classic samples have been produced at Madawaska Mine , near Bancroft, Ontario . Bedding parallel veins of fibrous calcite, often referred to in quarrying parlance as beef , occur in dark organic rich mudstones and shales, these veins are formed by increasing fluid pressure during diagenesis . Calcite formation can proceed by several pathways, from
Tarphyceratidae - Misplaced Pages Continue
1600-472: The classical terrace ledge kink model to the crystallization of poorly ordered precursor phases like amorphous calcium carbonate (ACC) via an Ostwald ripening process, or via the agglomeration of nanocrystals. The crystallization of ACC can occur in two stages. First, the ACC nanoparticles rapidly dehydrate and crystallize to form individual particles of vaterite . Second, the vaterite transforms to calcite via
1650-437: The expansion and eventual collapse of cave systems, resulting in various forms of karst topography . Calcite exhibits an unusual characteristic called retrograde solubility: it is less soluble in water as the temperature increases. Calcite is also more soluble at higher pressures. Pure calcite has the composition CaCO 3 . However, the calcite in limestone often contains a few percent of magnesium . Calcite in limestone
1700-484: The following reaction The carbon dioxide released by this reaction produces a characteristic effervescence when a calcite sample is treated with an acid. Due to its acidity, carbon dioxide has a slight solubilizing effect on calcite. The overall reaction is If the amount of dissolved carbon dioxide drops, the reaction reverses to precipitate calcite. As a result, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on such factors as
1750-732: The glow curve peaks, it was found that Pb and Mn acted as activators in the calcite lattice, but Pb was much less efficient than Mn . Measuring mineral thermoluminescence experiments usually use x-rays or gamma-rays to activate the sample and record the changes in glowing curves at a temperature of 700–7500 K. Mineral thermoluminescence can form various glow curves of crystals under different conditions, such as temperature changes, because impurity ions or other crystal defects present in minerals supply luminescence centers and trapping levels. Observing these curve changes also can help infer geological correlation and age determination. Calcite, like most carbonates, dissolves in acids by
1800-626: The impression is slight, running along the dorsal median. The Tarphyceratidae are known mainly from the Lower Ordovician (M-U Canad); gave rise to the Trocholitidae and provided the sources for the more advanced barrandeocerids Genera in the Tarphyeratidae as named in the Treatise on Invertebrate Paleontology Part K (Furnish and Glenister 1964) are restricted to the middle and upper parts of
1850-427: The ocean at the time they became mineralised, and retained this mineralogy for the remainder of their evolutionary history. Petrographic evidence for these calcite sea conditions consists of calcitic ooids , lmc cements, hardgrounds , and rapid early seafloor aragonite dissolution. The evolution of marine organisms with calcium carbonate shells may have been affected by the calcite and aragonite sea cycle. Calcite
1900-514: The primary inorganic precipitate of calcium carbonate in marine waters was low-magnesium calcite (lmc), as opposed to the aragonite and high-magnesium calcite (hmc) precipitated today. Calcite seas alternated with aragonite seas over the Phanerozoic , being most prominent in the Ordovician and Jurassic periods. Lineages evolved to use whichever morph of calcium carbonate was favourable in
1950-446: The rhombohedron form. Its fracture is conchoidal , but difficult to obtain. Scalenohedral faces are chiral and come in pairs with mirror-image symmetry; their growth can be influenced by interaction with chiral biomolecules such as L- and D- amino acids . Rhombohedral faces are not chiral. Calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence . A transparent variety called " Iceland spar "
2000-420: The septae or connecting rings. In most fossil nautiluses, the siphuncle runs more or less through the center of each chamber, but in ammonites and belemnites it usually runs along the ventral edge of the shell. In some fossil straight shelled nautiloids, cylindrical calcareous growths ("siphuncular deposits") around the siphuncle can be seen towards the apex of the shell. These were apparently counterweights for
2050-677: The siphuncle. Connecting rings are typically continuous with the septal necks, and are difficult to distinguish without close examination. However, their developmental origin is wholly separate from the shell and septa, and they utilize calcite rather than aragonite as a biomineralized reinforcement. Biomineralized structures which develop within the siphuncle are known as endosiphuncular deposits (or simply siphonal deposits). These may include horizontal partitions ( diaphragms ), stacked conical structures ( endocones ), longitudinal rods, and various other concretions. Endosiphuncular deposits are typically thin structures which may be homologous to parts of
Tarphyceratidae - Misplaced Pages Continue
2100-433: The sky through the crystal and then rotating it so that the two images are of equal brightness, the rings of polarized light that surround the sun can be seen even under overcast skies. Identifying the sun's location would give seafarers a reference point for navigating on their lengthy sea voyages. In World War II, high-grade optical calcite was used for gun sights, specifically in bomb sights and anti-aircraft weaponry. It
2150-517: The soft body at the other end of the shell, and allowed the nautilus to swim in a horizontal position. Without these deposits, the apex of the buoyant shell would have pointed upwards and the heavier body downwards, making horizontal swimming difficult. The siphuncle of the Endocerida also contained much of the organisms' body organs. Calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO 3 ). It
2200-549: The subsurface in response to microorganism activity, such as sulfate -dependent anaerobic oxidation of methane , where methane is oxidized and sulfate is reduced , leading to precipitation of calcite and pyrite from the produced bicarbonate and sulfide . These processes can be traced by the specific carbon isotope composition of the calcites, which are extremely depleted in the C isotope, by as much as −125 per mil PDB (δ C). Calcite seas existed in Earth's history when
2250-417: The term alabaster because of the close association. Many other cultures have used the material for similar carved objects and applications. A transparent variety of calcite known as Iceland spar may have been used by Vikings for navigating on cloudy days. A very pure crystal of calcite can split a beam of sunlight into dual images, as the polarized light deviates slightly from the main beam. By observing
2300-457: The type of weathering the substrate experienced: growth on physically weathered surfaces has a shingled morphology due to Volmer-Weber growth, growth on chemically weathered surfaces has characteristics of Stranski-Krastanov growth, and growth on pristine cleavage surfaces has characteristics of Frank - van der Merwe growth. These differences are apparently due to the influence of surface roughness on layer coalescence dynamics. Calcite may form in
2350-495: The water temperature, pH , and dissolved ion concentrations. When conditions are right for precipitation, calcite forms mineral coatings that cement rock grains together and can fill fractures. When conditions are right for dissolution, the removal of calcite can dramatically increase the porosity and permeability of the rock, and if it continues for a long period of time, may result in the formation of caves . Continued dissolution of calcium carbonate-rich formations can lead to
2400-405: The {1 0 1} or {1 0 4} directions (the most common cleavage plane). Habits include acute to obtuse rhombohedra, tabular habits, prisms , or various scalenohedra . Calcite exhibits several twinning types that add to the observed habits. It may occur as fibrous, granular, lamellar, or compact. A fibrous, efflorescent habit is known as lublinite . Cleavage is usually in three directions parallel to
2450-426: Was conducted by adding activators such as ions of Mn, Fe, Co, Ni, Cu, Zn, Ag, Pb, and Bi to the calcite samples to observe whether they emitted heat or light. The results showed that adding ions ( Cu , Cu , Zn , Ag , Bi , Fe , Fe , Co , Ni ) did not react. However, a reaction occurred when both manganese and lead ions were present in calcite. By changing the temperature and observing
2500-455: Was used as a polarizer (in Nicol prisms ) before the invention of Polaroid plates and still finds use in optical instruments. Also, experiments have been conducted to use calcite for a cloak of invisibility . Microbiologically precipitated calcite has a wide range of applications, such as soil remediation, soil stabilization and concrete repair. It also can be used for tailings management and
#527472