A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei, can be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur; the substance involved in a chemical reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, they yield one or more products, which have properties different from the reactants. Reactions consist of a sequence of individual sub-steps, the so-called elementary reactions, the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, sometimes intermediate products and reaction conditions.
Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration. Reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium. Reactions that proceed in the forward direction to approach equilibrium are described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of free energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product. In biochemistry, a consecutive series of chemical reactions form metabolic pathways; these reactions are catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperatures and concentrations present within a cell.
The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays, reactions between elementary particles, as described by quantum field theory. Chemical reactions such as combustion in fire and the reduction of ores to metals were known since antiquity. Initial theories of transformation of materials were developed by Greek philosophers, such as the Four-Element Theory of Empedocles stating that any substance is composed of the four basic elements – fire, water and earth. In the Middle Ages, chemical transformations were studied by Alchemists, they attempted, in particular, to convert lead into gold, for which purpose they used reactions of lead and lead-copper alloys with sulfur. The production of chemical substances that do not occur in nature has long been tried, such as the synthesis of sulfuric and nitric acids attributed to the controversial alchemist Jābir ibn Hayyān; the process involved heating of sulfate and nitrate minerals such as copper sulfate and saltpeter.
In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid and sodium chloride. With the development of the lead chamber process in 1746 and the Leblanc process, allowing large-scale production of sulfuric acid and sodium carbonate chemical reactions became implemented into the industry. Further optimization of sulfuric acid technology resulted in the contact process in the 1880s, the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, Isaac Newton tried to establish theories of the experimentally observed chemical transformations; the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of a fire-like element called "phlogiston", contained within combustible bodies and released during combustion; this proved to be false in 1785 by Antoine Lavoisier who found the correct explanation of the combustion as reaction with oxygen from the air.
Joseph Louis Gay-Lussac recognized in 1808 that gases always react in a certain relationship with each other. Based on this idea and the atomic theory of John Dalton, Joseph Proust had developed the law of definite proportions, which resulted in the concepts of stoichiometry and chemical equations. Regarding the organic chemistry, it was long believed that compounds obtained from living organisms were too complex to be obtained synthetically. According to the concept of vitalism, organic matter was endowed with a "vital force" and distinguished from inorganic materials; this separation was ended however by the synthesis of urea from inorganic precursors by Friedrich Wöhler in 1828. Other chemists who brought major contributions to organic chemistry include Alexander William Williamson with his synthesis of ethers and Christopher Kelk Ingold, among many discoveries, established the mechanisms of substitution reactions. Chemical equations are used to graphically illustrate chemical reactions, they consist of chemical or structural formulas of the reactants on the left and those of the products on the right.
They are separated by an arrow which indicates the type of the reaction.
Chemiluminescence is the emission of light, as the result of a chemical reaction. There may be limited emission of heat. Given reactants A and B, with an excited intermediate ◊, + → → + lightFor example, if is luminol and is hydrogen peroxide in the presence of a suitable catalyst we have: C 8 H 7 N 3 O 2 luminol + H 2 O 2 hydrogen peroxide ⟶ 3 − APA ⟶ 3 − APA + light where: 3-APA is 3-aminophthalate 3-APA is the vibronic excited state fluorescing as it decays to a lower energy level; the decay of this excited state to a lower energy level causes light emission. In theory, one photon of light should be given off for each molecule of reactant; this is equivalent to Avogadro's number of photons per mole of reactant. In actual practice, non-enzymatic reactions exceed 1% QC, quantum efficiency. In a chemical reaction, reactants collide to form a transition state, the enthalpic maximum in a reaction coordinate diagram, which proceeds to the product. Reactants form products of lesser chemical energy.
The difference in energy between reactants and products, represented as Δ H r x n, is turned into heat, physically realized as excitations in the vibrational state of the normal modes of the product. Since vibrational energy is much greater than the thermal agitation, it disperses in the solvent through molecular rotation; this is. In a chemiluminescent reaction, the direct product of the reaction is an excited electronic state; this state decays into an electronic ground state and emits light through either an allowed transition or a forbidden transition, depending on the spin state of the electronic excited state formed. Chemiluminescence differs from fluorescence or phosphorescence in that the electronic excited state is the product of a chemical reaction rather than of the absorption of a photon, it is the antithesis of a photochemical reaction, in which light is used to drive an endothermic chemical reaction. Here, light is generated from a chemically exothermic reaction; the chemiluminescence might be induced by an electrochemical stimulus, in this case is called electrochemiluminescence.
A standard example of chemiluminescence in the laboratory setting is the luminol test. Here, blood is indicated by luminescence upon contact with iron in hemoglobin; when chemiluminescence takes place in living organisms, the phenomenon is called bioluminescence. A light stick emits light by chemiluminescence. Chemiluminescence in aqueous system is caused by redox reactions. Luminol in an alkaline solution with hydrogen peroxide in the presence of iron or copper, or an auxiliary oxidant, produces chemiluminescence; the luminol reaction is C 8 H 7 N 3 O 2 luminol + H 2 O 2 hydrogen peroxide ⟶ 3 − APA ⟶ 3 − APA + light One of the oldest known chemiluminescent reactions is that of elemental white phosphorus oxidizing in moist air, producing a green glow. This is a gas-phase reaction of phosphorus vapor, above the solid, with oxygen producing the excited states 2 and HPO. Another gas phase reaction is the basis of nitric oxide detection in commercial analytic instruments applied to environmental air-quality testing.
Ozone is combined with nitric oxide to form nitrogen dioxide in an activated state. NO+O3 → NO2+ O2The activated NO2 luminesces broadband visible to infrared light as it reverts to a lower energy state. A photomultiplier and associated electronics counts the photons that are proportional to the amount of NO present. To determine the amount of nitrogen dioxide, NO2, in a sample it must first be converted to nitric oxide, NO, by passing the sample through a converter before the above ozone activation reaction is applied; the ozone reaction produces a photon count proportional to NO, proportional to NO2 before it was converted to NO. In the case of a mixed sample that contains both NO and NO2, the above reaction yields the amount of NO and NO2 combined in the air sample, assuming that the sample is passed through the converter. If the mixed sample is not passed through the converter, the ozone reaction produces activated NO2 only in proportion to the NO in the sample; the NO2 in the sample is not activated by the ozone reaction.
Though unactivated NO2 is present with the activated NO2, photons are emitted only by the activated species, proportional to original NO. Final step: Subtract NO from to yield NO2 In chemical kinetics, infrared chemiluminiscence refers to the e
Wulfenite is a lead molybdate mineral with the formula PbMoO4. It can be most found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be variable. In its yellow form it is sometimes called "yellow lead ore", it crystallizes in the tetragonal system occurring as stubby, pyramidal or tabular crystals. It occurs as earthy, granular masses, it is found in many localities, associated with lead ores as a secondary mineral associated with the oxidized zone of lead deposits. It is a secondary ore of molybdenum, is sought by collectors. Wulfenite was first described in 1845 for an occurrence in Bad Bleiberg, Austria, it was named for an Austrian mineralogist. It occurs as a secondary mineral in oxidized hydrothermal lead deposits, it occurs with cerussite, smithsonite, vanadinite, mimetite, descloizite and various iron and manganese oxides. A noted locality for wulfenite is the Red Cloud Mine in Arizona. Crystals are deep red in color and very well-formed.
The Los Lamentos locality in Mexico produced thick tabular orange crystals. Another locality is Mount Peca in Slovenia; the crystals are yellow with well-developed pyramids and bipyramids. In 1997, the crystal was depicted on a stamp by the Post of Slovenia. Lesser known localities of wulfenite include: Sherman Tunnel, St. Peter’s Dome, Tincup-Tomichi-Moncarch mining districts, Pride of America mine and Bandora mine in Colorado. Small crystals occur in Bulwell and Kirkby-in-Ashfield, England; these crystals occur in a galena-wulfenite-uraniferous asphaltite horizon in a magnesian limestone. The wulfenite found in this area is similar in properties to the wulfenites of the Alps and may be similar in origin. Wulfenite possesses nearly equal axial ratios. Wulfenite is classed by a pyramidal-hemihedral crystal symmetry. Therefore, the unit cell is formed by placing points at the vertices and centers of the faces of rhomboids with square bases and the crystallographic axes coincide in directions with the edges of the rhomboids.
Two of these lattices interpenetrate such that a point on the first is diagonal to the second and one quarter the distance between the two seconds. An extensive solid solution exists between the two end members wulfenite and stolzite, such that tungstenian-wulfenite compositions range from 90% wulfenite and 10% stolzite to chillagite and so on; the Commission for New Minerals and Mineral Names of the International Mineralogical Association has deemed that the solid solutions do not require new names. The correct nomenclature of the 90:10 solid state is wulfenite-I41/a and the 64:36 solid state is wulfenite-I4; the structure of the wulfenite-I41/a system can be described as a close packing of tetrahedral MoO42− anions and Pb2+ cations. In the lattice, the MoO42− anions are distorted, though the bond lengths remain equal and the oxygens are linked through Pb-O bonds; each lead atom has an 8-coordination with oxygen and two different Pb-O bond distances. This structure resembles that of pure wulfenite.
The structure of wulfenite-I4 is very similar to that of wulfenite-I41/a but has an unequal distribution of tungsten and molybdenum which may explain the observed hemihedrism. It is argued that no miscibility gap exists in the wulfenite-stolzite solid solution at room temperature due to the identical size and shape of the MoO42− and WO42− ions, arguments have been made for the existence of a miscibility gap at higher temperatures; the crystals of wulfenite are more tabular and thinner than those of scheelite, the more pyramidal and prismatic crystals show distinct hemimorphism. The heat capacity and enthalpy of wulfenite were determined taking into consideration the existence of solid solutions and the inclusion of impurities; the reported values are as follows: Cp° = 119.41±0.13 J/molK, S° = J/molK, ΔH°= J/mol. When forced through a tube into a flame, wulfenite disintegrates audibly and fuses readily. With the salt of phosphorus, it yields molybdenum beads. With soda on charcoal it yields a lead globule.
When the powdered mineral is evaporated with HCl, molybdic oxide is formed. Molybdenum can be extracted from wulfenite by crushing the ore to 60-80 mesh, mixing the ore with NaNO3 or NaOH, heating the mixture to about 700 °C, leaching with water, collecting the insoluble residues which may include Fe, Al, Zn, Cu, Mn, Pb, Au and Ag the NaMoO4 solution is agitated with a solution of MgCl2, filtered, CaCl2 or FeCl2 or any other chlorides is added to the Mo solution and heated and agitated and the desired product is collected; the full process is patented by the Union Carbon Corp.. Wulfenite has been shown to form synthetically through the sintering of molybdite with cerussite as well as that of molybdite with lead oxide; the following will describe both methods of synthesis. Synthesis from molybdite and cerussite: Thermal analysis of the 1:1 mix of molybdite and cerussite first displayed the characteristic peaks of cerussite. There is a sharp endothermic peak at 300 °C, which occurs during the dehydration of hydrocerussite associated with cerussite.
A second peak at 350 °C is the first step of cerussite’s dissociation into PbO*PbCO3. At 400 °C, a medium endothermic peak represents the second step of the dissociation into lead oxide; these transit
Triboluminescence is an optical phenomenon in which light is generated through the breaking of chemical bonds in a material when it is pulled apart, scratched, crushed, or rubbed. The phenomenon is not understood, but appears to be caused by the separation and reunification of electrical charges; the term comes from the Latin lumen. Triboluminescence can be observed when peeling adhesive tapes. Triboluminescence is used as a synonym for fractoluminescence. Triboluminescence differs from piezoluminescence in that a piezoluminescent material emits light when it is deformed, as opposed to broken; these are examples of mechanoluminescence, luminescence resulting from any mechanical action on a solid. The Uncompahgre Ute Indians from Central Colorado are one of the first documented groups of people in the world credited with the application of mechanoluminescence involving the use of quartz crystals to generate light; the Ute constructed special ceremonial rattles made from buffalo rawhide which they filled with clear quartz crystals collected from the mountains of Colorado and Utah.
When the rattles were shaken at night during ceremonies, the friction and mechanical stress of the quartz crystals impacting together produced flashes of light visible through the translucent buffalo hide. The first recorded observation is attributed to English scholar Francis Bacon when he recorded in his 1620 Novum Organum that "It is well known that all sugar, whether candied or plain, if it be hard, will sparkle when broken or scraped in the dark." The scientist Robert Boyle reported on some of his work on triboluminescence in 1663. In the late 1790s, sugar production began to produce more refined sugar crystals; these crystals were formed into a large solid cone for sale. This solid cone of sugar had to be broken into usable chunks using a device known as sugar nips. People began to notice. A important instance of triboluminescence occurred in Paris in 1675. Astronomer Jean-Felix Picard observed, his barometer consisted of a glass tube, filled with mercury. Whenever the mercury slid down the glass tube, the empty space above the mercury would glow.
While investigating this phenomenon, researchers discovered that static electricity could cause low-pressure air to glow. This discovery revealed the possibility of electric lighting. Materials scientists have not yet arrived at a full understanding of the effect, but the current theory of triboluminescence — based upon crystallographic and other experimental evidence — is that upon fracture of asymmetrical materials, charge is separated; when the charges recombine, the electrical discharge ionizes the surrounding air, causing a flash of light. Research further suggests that crystals which display triboluminescence must lack symmetry and be poor conductors. However, there are substances which break this rule, which do not possess asymmetry, yet display triboluminescence anyway, such as hexakisterbium iodide, it is thought. The biological phenomenon of triboluminescence is conditioned by recombination of free radicals during mechanical activation. A diamond may begin to glow; this happens to diamonds while a facet is being ground or the diamond is being sawn during the cutting process.
Diamonds may fluoresce red. Some other minerals, such as quartz, are triboluminescent. Ordinary Pressure-sensitive tape displays a glowing line where the end of the tape is being pulled away from the roll. In 1953, Soviet scientists observed; the mechanism of X-ray generation was studied further in 2008. Similar X-Ray emissions have been observed with metals; when sugar crystals are crushed, tiny electrical fields are created, separating positive and negative charges that create sparks while trying to reunite. Wint-O-Green Life Savers work well for creating such sparks, because wintergreen oil is fluorescent and converts ultraviolet light into blue light. Triboluminescence is a biological phenomenon observed in mechanical deformation and contact electrization of epidermal surface of osseous and soft tissues, at chewing food, at friction in joints of vertebrae, during sexual intercourse, during blood circulation. Fractoluminescence is used as a synonym for triboluminescence, it is the emission of light from the fracture of a crystal, but fracturing occurs with rubbing.
Depending upon the atomic and molecular composition of the crystal, when the crystal fractures a charge separation can occur making one side of the fractured crystal positively charged and the other side negatively charged. Like in triboluminescence, if the charge separation results in a large enough electric potential, a discharge across the gap and through the bath gas between the interfaces can occur; the potential at which this occurs depends upon the dielectric properties of the bath gas. The emission of electromagnetic radiation during plastic deformation and crack propagation in metals and rocks have been studied; the EMR emissions from metals and alloys have been explored and confirmed. Molotskii presented a dislocation mechanism for this type of EMR emissions. Sril
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
Atmospheric pressure, sometimes called barometric pressure, is the pressure within the atmosphere of Earth. The standard atmosphere is a unit of pressure defined as 1013.25 mbar, equivalent to 760 mmHg, 29.9212 inches Hg, or 14.696 psi. The atm unit is equivalent to the mean sea-level atmospheric pressure on Earth, that is, the Earth's atmospheric pressure at sea level is 1 atm. In most circumstances atmospheric pressure is approximated by the hydrostatic pressure caused by the weight of air above the measurement point; as elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. Pressure measures force per unit area, with SI units of Pascals. On average, a column of air with a cross-sectional area of 1 square centimetre, measured from mean sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons or 2.37 lbf, resulting in a pressure at sea level of about 10.1 N/cm2 or 101 kN/m2.
A column of air with a cross-sectional area of 1 in2 would have a mass of about 6.65 kg and a weight of about 65.4 N or 14.7 lbf, resulting in a pressure of 10.1 N/cm2 or 14.7 lbf/in2. Atmospheric pressure is caused by the gravitational attraction of the planet on the atmospheric gases above the surface, is a function of the mass of the planet, the radius of the surface, the amount and composition of the gases and their vertical distribution in the atmosphere, it is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition. The mean sea-level pressure is the average atmospheric pressure at mean sea level; this is the atmospheric pressure given in weather reports on radio and newspapers or on the Internet. When barometers in the home are set to match the local weather reports, they measure pressure adjusted to sea level, not the actual local atmospheric pressure; the altimeter setting in aviation is an atmospheric pressure adjustment.
Average sea-level pressure is 1013.25 mbar. In aviation, weather reports, QNH is transmitted around the world in millibars or hectopascals, except in the United States and Colombia where it is reported in inches of mercury; the United States and Canada report sea-level pressure SLP, adjusted to sea level by a different method, in the remarks section, not in the internationally transmitted part of the code, in hectopascals or millibars. However, in Canada's public weather reports, sea level pressure is instead reported in kilopascals. In the US weather code remarks, three digits are all; the highest sea-level pressure on Earth occurs in Siberia, where the Siberian High attains a sea-level pressure above 1050 mbar, with record highs close to 1085 mbar. The lowest measurable sea-level pressure is found at the centers of tropical cyclones and tornadoes, with a record low of 870 mbar. Surface pressure is the atmospheric pressure at a location on Earth's surface, it is directly proportional to the mass of air over that location.
For numerical reasons, atmospheric models such as general circulation models predict the nondimensional logarithm of surface pressure. The average value of surface pressure on Earth is 985 hPa; this is in contrast to mean sea-level pressure, which involves the extrapolation of pressure to sea-level for locations above or below sea-level. The average pressure at mean sea-level in the International Standard Atmosphere is 1013.25 hPa, or 1 atmosphere, or 29.92 inches of mercury. Pressure and the acceleration due to gravity, are related by P = F/A = /A, where A is surface area. Atmospheric pressure is thus proportional to the weight per unit area of the atmospheric mass above that location. Pressure on Earth varies with the altitude of the surface. Pressure varies smoothly from the Earth's surface to the top of the mesosphere. Although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round; as altitude increases, atmospheric pressure decreases.
One can calculate the atmospheric pressure at a given altitude. Temperature and humidity affect the atmospheric pressure, it is necessary to know these to compute an accurate figure; the graph at right was developed for a temperature of 15 °C and a relative humidity of 0%. At low altitudes above sea level, the pressure decreases by about 1.2 kPa for every 100 metres. For higher altitudes within the troposphere, the following equation relates atmospheric pressure p to altitude h p = p 0 ⋅ g ⋅ M R 0 ⋅
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be seen or examined closely. However, in places where the overlying cover is removed through erosion or tectonic uplift, the rock may be exposed, or crop out; such exposure will happen most in areas where erosion is rapid and exceeds the weathering rate such as on steep hillsides, mountain ridges and tops, river banks, tectonically active areas. In Finland, glacial erosion during the last glacial maximum, followed by scouring by sea waves, followed by isostatic uplift has produced a large number of smooth coastal and littoral outcrops. Bedrock and superficial deposits may be exposed at the Earth's surface due to human excavations such as quarrying and building of transport routes. Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis and creating geologic maps.
In situ measurements are critical for proper analysis of geological history and outcrops are therefore important for understanding the geologic time scale of earth history. Some of the types of information that cannot be obtained except from bedrock outcrops or by precise drilling and coring operations, are structural geology features orientations, depositional features orientations, paleomagnetic orientations. Outcrops are very important for understanding fossil assemblages, paleo-environment, evolution as they provide a record of relative changes within geologic strata. Accurate description and sampling for laboratory analysis of outcrops made possible all of the geologic sciences and the development of fundamental geologic laws such as the law of superposition, the principle of original horizontality, principle of lateral continuity, the principle of faunal succession. On Ordnance Survey maps in Great Britain, cliffs are distinguished from outcrops: cliffs have a continuous line along the top edge with lines protruding down.
An outcrop example in California is the Vasquez Rocks, familiar from location shooting use in many films, composed of uplifted sandstone. Yana is another example of outcrops, located in Uttara Kannada district in India. Digital outcrop model List of rock formations Geological formation Geologic time scale Media related to Outcrops at Wikimedia Commons