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67-466: The bed of Snowy River is covered with bright white calcite . Over time, ancient, slow moving ground water dissolved the limestone walls of the cave and, with the help of microorganisms , recrystallized limestone into the white-colored mineral. Since prehistoric times, ground water saturated with dissolved calcite has periodically flooded the cave, followed by extended periods of dryness, leaving behind coatings and deposits. Fort Stanton Cave, now including

134-433: A 2 and a 3 as Hence zone indices of the direction perpendicular to plane ( hkℓ ) are, in suitably normalized triplet form, simply [ 2 h + k , h + 2 k , ℓ ( 3 / 2 ) ( a / c ) 2 ] {\displaystyle [2h+k,h+2k,\ell (3/2)(a/c)^{2}]} . When four indices are used for the zone normal to plane ( hkℓ ), however,

201-687: 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 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

268-436: 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

335-421: A , b and c appropriately: divide by the largest of the three numbers, and then multiply by the least common denominator . Thus, integer Miller indices implicitly include indices with all rational ratios. The reason why planes where the components (in the reciprocal-lattice basis) have rational ratios are of special interest is that these are the lattice planes : they are the only planes whose intersections with

402-607: 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

469-423: A defining Mohs hardness of 3, 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

536-405: 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

603-468: A new book 12 Miles From Daylight with over 300 pages and 350 photographs and maps, featuring explorations from 1855 to the present. From crusts on the cave walls, antibiotic-producing actinobacteria and some 36 strains of manganese-using bacteria have been discovered. New Mexico Institute of Mining and Technology says the organisms live in this isolated environment by chemically breaking down manganese compounds, creating reconstituted mineral byproducts in

670-775: A notation system in crystallography for lattice planes in crystal (Bravais) lattices . In particular, a family of lattice planes of a given (direct) Bravais lattice is determined by three integers h , k , and  ℓ , the Miller indices . They are written ( hkℓ ), and denote the family of (parallel) lattice planes (of the given Bravais lattice) orthogonal to g h k ℓ = h b 1 + k b 2 + ℓ b 3 {\displaystyle \mathbf {g} _{hk\ell }=h\mathbf {b} _{1}+k\mathbf {b} _{2}+\ell \mathbf {b} _{3}} , where b i {\displaystyle \mathbf {b} _{i}} are

737-478: A reciprocal lattice vector. The requirement of lowest terms means that it is the shortest reciprocal lattice vector in the given direction. Equivalently, ( hkℓ ) denotes a plane that intercepts the three points a 1 / h , a 2 / k , and a 3 / ℓ , or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane, in the basis of the lattice vectors. If one of

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804-526: 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

871-441: 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 ,

938-437: 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

1005-741: 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

1072-459: 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

1139-473: Is important to determine the planes and thus to have a notation system. Ordinarily, Miller indices are always integers by definition, and this constraint is physically significant. To understand this, suppose that we allow a plane ( abc ) where the Miller "indices" a , b and c (defined as above) are not necessarily integers. If a , b and c have rational ratios, then the same family of planes can be written in terms of integer indices ( hkℓ ) by scaling

1206-524: Is known as lublinite . Cleavage is usually in three directions parallel to 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 "

1273-475: Is marked by Miller indices . By convention, negative integers are written with a bar, as in 3 for −3. The integers are usually written in lowest terms, i.e. their greatest common divisor should be 1. Miller indices are also used to designate reflections in X-ray crystallography . In this case the integers are not necessarily in lowest terms, and can be thought of as corresponding to planes spaced such that

1340-757: 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

1407-554: 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

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1474-403: 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

1541-474: 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

1608-586: 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)

1675-524: 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

1742-448: The a 1 , a 2 , c {\displaystyle a_{1},a_{2},c} directions, or four Bravais–Miller indices h, k, i, l in 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

1809-419: The basis or primitive translation vectors of the reciprocal lattice for the given Bravais lattice. (Note that the plane is not always orthogonal to the linear combination of direct or original lattice vectors h a 1 + k a 2 + ℓ a 3 {\displaystyle h\mathbf {a} _{1}+k\mathbf {a} _{2}+\ell \mathbf {a} _{3}} because

1876-400: The direction : That is, it uses the direct lattice basis instead of the reciprocal lattice. Note that [hkℓ] is not generally normal to the ( hkℓ ) planes, except in a cubic lattice as described below. For the special case of simple cubic crystals, the lattice vectors are orthogonal and of equal length (usually denoted a ), as are those of the reciprocal lattice. Thus, in this common case,

1943-489: The Miller indices ( hkℓ ) and [ hkℓ ] both simply denote normals/directions in Cartesian coordinates . For cubic crystals with lattice constant a , the spacing d between adjacent ( hkℓ ) lattice planes is (from above) Because of the symmetry of cubic crystals, it is possible to change the place and sign of the integers and have equivalent directions and planes: For face-centered cubic and body-centered cubic lattices,

2010-560: The Snowy River Passage, contains the fourth largest cave footprint (the area within a convex polygon that encloses the known cave passages) in the USA. The Bureau of Land Management reports that Snowy River may be the largest continuous cave formation in America. Discovered in 2001, Snowy River is a section of a much larger cave complex. Researchers and explorers have not yet determined how

2077-431: The [ 1 1 0] directions are really similar. If S is the intercept of the plane with the [ 1 1 0] axis, then There are also ad hoc schemes (e.g. in the transmission electron microscopy literature) for indexing hexagonal lattice vectors (rather than reciprocal lattice vectors or planes) with four indices. However they do not operate by similarly adding a redundant index to the regular three-index set. For example,

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2144-707: The air. The total amount of artificial CO 2 absorbed by the oceans is calculated to be 118 ± 19 Gt C. If a large amount of CO 2 dissolves in the sea, it will cause the acidity of the seawater to increase, thereby affecting the pH value of the ocean. Calcifying organisms in the sea, such as molluscs foraminifera, crustaceans, echinoderms and corals, are susceptible to pH changes. Meanwhile, these calcifying organisms are also an essential source of calcite. As ocean acidification causes pH to drop, carbonate ion concentrations will decline, potentially reducing natural calcite production. Miller index#Case of hexagonal and rhombohedral structures Miller indices form

2211-690: 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

2278-472: 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

2345-411: 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 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

2412-445: The corresponding Miller indices, and i is a redundant index. This four-index scheme for labeling planes in a hexagonal lattice makes permutation symmetries apparent. For example, the similarity between (110) ≡ (11 2 0) and (1 2 0) ≡ (1 2 10) is more obvious when the redundant index is shown. In the figure at right, the (001) plane has a 3-fold symmetry: it remains unchanged by a rotation of 1/3 (2 π /3 rad, 120°). The [100], [010] and

2479-438: The crystal are 2d-periodic. For a plane (abc) where a , b and c have irrational ratios, on the other hand, the intersection of the plane with the crystal is not periodic. It forms an aperiodic pattern known as a quasicrystal . This construction corresponds precisely to the standard "cut-and-project" method of defining a quasicrystal, using a plane with irrational-ratio Miller indices. (Although many quasicrystals, such as

2546-456: The direct lattice vectors need not be mutually orthogonal.) This is based on the fact that a reciprocal lattice vector g {\displaystyle \mathbf {g} } (the vector indicating a reciprocal lattice point from the reciprocal lattice origin) is the wavevector of a plane wave in the Fourier series of a spatial function (e.g., electronic density function) which periodicity follows

2613-437: 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

2680-484: 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

2747-422: The formations relate to the geology and hydrology. After visits to the dry riverbed in 2001, 2003 and 2005, explorers were surprised to find Snowy River flowing with water in 2007 and also in 2010 after a heavy winter snowfall. In 2014, cave surveys reached points as far as 12 miles (19.3 km) from daylight from the cave's single entrance. In August 2014, Snowy River again started flowing and continued to flow for

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2814-732: 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

2881-464: The hexagonal {2 1 1} directions (morphological unit cell) or {2 1 4} directions (structural unit cell); and rhombohedral, with faces in 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

2948-569: The indices is zero, it means that the planes do not intersect that axis (the intercept is "at infinity"). Considering only ( hkℓ ) planes intersecting one or more lattice points (the lattice planes ), the perpendicular distance d between adjacent lattice planes is related to the (shortest) reciprocal lattice vector orthogonal to the planes by the formula: d = 2 π / | g h k ℓ | {\displaystyle d=2\pi /|\mathbf {g} _{hk\ell }|} . The related notation [hkℓ] denotes

3015-501: The lattice vectors. Both definitions are given below. In either case, one needs to choose the three lattice vectors a 1 , a 2 , and a 3 that define the unit cell (note that the conventional unit cell may be larger than the primitive cell of the Bravais lattice , as the examples below illustrate). Given these, the three primitive reciprocal lattice vectors are also determined (denoted b 1 , b 2 , and b 3 ). Then, given

3082-406: The left. And, note that for hexagonal interplanar distances, they take the form Crystallographic directions are lines linking nodes ( atoms , ions or molecules ) of a crystal. Similarly, crystallographic planes are planes linking nodes. Some directions and planes have a higher density of nodes; these dense planes have an influence on the behavior of the crystal: For all these reasons, it

3149-463: The literature often uses [ h , k , − h − k , ℓ ( 3 / 2 ) ( a / c ) 2 ] {\displaystyle [h,k,-h-k,\ell (3/2)(a/c)^{2}]} instead. Thus as you can see, four-index zone indices in square or angle brackets sometimes mix a single direct-lattice index on the right with reciprocal-lattice indices (normally in round or curly brackets) on

3216-510: The minerals aragonite and vaterite . Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, and vaterite 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

3283-456: The next three years, severely limiting exploration far upstream past Midnight Junction where a camping area had been established. With surveyed passage reaching 31.59 miles (50.84 km) in 2017, this cave is the third longest cave in New Mexico. At 11 miles, Snowy River is the world's longest calcite formation. The non-profit [1] group has a long history of work in the cave, and in 2017 published

3350-427: 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

3417-531: The original Bravais lattice, so wavefronts of the plane wave are coincident with parallel lattice planes of the original lattice. Since a measured scattering vector in X-ray crystallography , Δ k = k o u t − k i n {\displaystyle \Delta \mathbf {k} =\mathbf {k} _{\mathrm {out} }-\mathbf {k} _{\mathrm {in} }} with k o u t {\displaystyle \mathbf {k} _{\mathrm {out} }} as

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3484-554: The outgoing (scattered from a crystal lattice) X-ray wavevector and k i n {\displaystyle \mathbf {k} _{\mathrm {in} }} as the incoming (toward the crystal lattice) X-ray wavevector, is equal to a reciprocal lattice vector g {\displaystyle \mathbf {g} } as stated by the Laue equations , the measured scattered X-ray peak at each measured scattering vector Δ k {\displaystyle \Delta \mathbf {k} }

3551-514: 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

3618-553: The primitive lattice vectors are not orthogonal. However, in these cases the Miller indices are conventionally defined relative to the lattice vectors of the cubic supercell and hence are again simply the Cartesian directions. With hexagonal and rhombohedral lattice systems , it is possible to use the Bravais–Miller system, which uses four indices ( h k i ℓ ) that obey the constraint Here h , k and ℓ are identical to

3685-640: The process that may have pharmaceutical uses. Scientists anticipate new biological as well as geologic discoveries will be found. Calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO 3 ). It 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

3752-406: The reciprocal lattice vector ( hkℓ ) as suggested above can be written in terms of reciprocal lattice vectors as h b 1 + k b 2 + ℓ b 3 {\displaystyle h\mathbf {b} _{1}+k\mathbf {b} _{2}+\ell \mathbf {b} _{3}} . For hexagonal crystals this may be expressed in terms of direct-lattice basis-vectors a 1 ,

3819-633: The reflections from adjacent planes would have a phase difference of exactly one wavelength (2 π ), regardless of whether there are atoms on all these planes or not. There are also several related notations: In the context of crystal directions (not planes), the corresponding notations are: Note, for Laue–Bragg interferences Miller indices were introduced in 1839 by the British mineralogist William Hallowes Miller , although an almost identical system ( Weiss parameters ) had already been used by German mineralogist Christian Samuel Weiss since 1817. The method

3886-433: 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

3953-549: 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

4020-417: 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

4087-400: The three Miller indices h , k , ℓ , ( h k ℓ ) {\displaystyle h,k,\ell ,(hk\ell )} denotes planes orthogonal to the reciprocal lattice vector: That is, ( hkℓ ) simply indicates a normal to the planes in the basis of the primitive reciprocal lattice vectors. Because the coordinates are integers, this normal is itself always

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4154-457: 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

4221-495: 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

4288-494: 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 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

4355-467: Was also historically known as the Millerian system, and the indices as Millerian, although this is now rare. The Miller indices are defined with respect to any choice of unit cell and not only with respect to primitive basis vectors, as is sometimes stated. There are two equivalent ways to define the meaning of the Miller indices: via a point in the reciprocal lattice , or as the inverse intercepts along

4422-426: 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

4489-455: 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

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