A laboratory is a facility that provides controlled conditions in which scientific or technological research and measurement may be performed. Laboratories used for scientific research take many forms because of the differing requirements of specialists in the various fields of science and engineering. A physics laboratory might contain a particle accelerator or vacuum chamber, while a metallurgy laboratory could have apparatus for casting or refining metals or for testing their strength. A chemist or biologist might use a wet laboratory, while a psychologist's laboratory might be a room with one-way mirrors and hidden cameras in which to observe behavior. In some laboratories, such as those used by computer scientists, computers are used for either simulations or the analysis of data. Scientists in other fields will use still other types of laboratories. Engineers use laboratories as well to design and test technological devices. Scientific laboratories can be found as research room and learning spaces in schools and universities, government, or military facilities, aboard ships and spacecraft.
Despite the underlying notion of the lab as a confined space for experts, the term "laboratory" is increasingly applied to workshop spaces such as Living Labs, Fab Labs, or Hackerspaces, in which people meet to work on societal problems or make prototypes, working collaboratively or sharing resources. This development is inspired by new, participatory approaches to science and innovation and relies on user-centred design methods and concepts like Open innovation or User innovation. One distinctive feature of work in Open Labs is phenomena of translation, driven by the different backgrounds and levels of expertise of the people involved. Early instances of "laboratories" recorded in English involved alchemy and the preparation of medicines; the emergence of Big Science during World War II increased the size of laboratories and scientific equipment, introducing particle accelerators and similar devices. The earliest laboratory according to the present evidence is a home laboratory of Pythagoras of Samos, the well-known Greek philosopher and scientist.
This laboratory was created when Pythagoras conducted an experiment about tones of sound and vibration of string. In the painting of Louis Pasteur by Albert Edelfelt in 1885, Louis Pasteur is shown comparing a note in his left hand with a bottle filled with a solid in his right hand, not wearing any personal protective equipment. Researching in teams started in the 19th century, many new kinds of equipment were developed in the 20th century. A 16th century underground alchemical laboratory was accidentally discovered in the year 2002. Rudolf II, Holy Roman Emperor was believed to be the owner; the laboratory is preserved as a museum in Prague. Laboratory techniques are the set of procedures used on natural sciences such as chemistry, physics to conduct an experiment, all of them follow the scientific method. Laboratory equipment refers to the various tools and equipment used by scientists working in a laboratory: The classical equipment includes tools such as Bunsen burners and microscopes as well as specialty equipment such as operant conditioning chambers, spectrophotometers and calorimeters.
Chemical laboratorieslaboratory glassware such as the beaker or reagent bottle Analytical devices as HPLC or spectrophotometersMolecular biology laboratories + Life science laboratoriesAutoclave Microscope Centrifuges Shakers & mixers Pipette Thermal cyclers Photometer Refrigerators and Freezers Universal testing machine ULT Freezers Incubators Bioreactor Biological safety cabinets Sequencing instruments Fume hoods Environmental chamber Humidifier Weighing scale Reagents Pipettes tips Polymer consumables for small volumes sterileLaboratory equipment is used to either perform an experiment or to take measurements and gather data. Larger or more sophisticated equipment is called a scientific instrument; the title of laboratory is used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories. These notably include: Film laboratory or Darkroom Clandestine lab for the production of illegal drugs Computer lab Crime lab used to process crime scene evidence Language laboratory Medical laboratory Public health laboratory Industrial laboratory In many laboratories, hazards are present.
Laboratory hazards might include poisons. Therefore, safety precautions are vitally important. Rules exist to minimize the individual's risk, safety equipment is used to protect the lab users from injury or to assist in responding to an emergency; the Occupational Safety and Health Administration in the United States, recognizing the unique characteristics of the laboratory workplace, has tailored a standard for occupational exposure to hazardous chemicals in laboratories. This standard is referred to as the "Laboratory Standard". Under this standard, a laboratory is required to produce a Chemical Hygiene Plan which addresses the specific hazards found in its location, its approach to them. In determining the proper Chemical Hygiene Plan for a particular business or laboratory, it is necessary to understand the requirements of the standard, evaluation of the current safety and environmental practi
Conoscopic interference pattern
This page is about the geology/optical mineralogy term. For general information about interference, see Interference or Interference patterns. A conoscopic interference pattern or interference figure is a pattern of birefringent colours crossed by dark bands, which can be produced using a geological petrographic microscope for the purposes of mineral identification and investigation of mineral optical and chemical properties; the figures are produced by optical interference when diverging light rays travel through an optically non-isotropic substance - that is, one in which the substance's refractive index varies in different directions within it. The figure can be thought of as a "map" of how the birefringence of a mineral would vary with viewing angle away from perpendicular to the slide, where the central colour is the birefringence seen looking straight down, the colours further from the centre equivalent to viewing the mineral at increasing angles from perpendicular; the dark bands correspond to positions.
In other words, the interference figure presents all possible birefringence colours for the mineral at once. Viewing the interference figure is a foolproof way to determine if a mineral is optically uniaxial or biaxial. If the figure is aligned use of a sensitive tint plate in conjunction with the microscope allows the user to determine mineral optic sign and optic angle. In optical mineralogy, a petrographic microscope and cross-polarised light are used to view the interference pattern; the thin section containing the mineral to be investigated is placed on the microscope stage, above one linear polariser, but with a second between the objective lens and the eyepiece. The microscope's condenser is brought up close underneath the specimen to produce a wide divergence of polarised rays through a small point, light intensity increased as much as possible. A high power objective lens is used; this both maximises the solid angle subtended by the lens, hence the angular variation of the light intercepted, increases the likelihood that only a single crystal will be viewed at any given time.
To view the figure, the light rays leaving the microscope must emerge less in parallel. This is achieved either by pulling out the eyepiece altogether, or by placing a Bertrand lens between the objective lens and the eyepiece. Any crystal section can in principle produce an interference pattern. However, in practice, only a few different crystallographic orientations are both 1. Convenient to identify, to allow a figure to be produced, 2. Able to produce reliable information about crystal properties; the most useful and obtainable orientation is one looking down the optic axis of a crystal section, which yields a figure referred to as an optic axis figure. Such crystal orientations are findable in thin section by looking for slices through minerals which are not isotropic but that appear uniformly black or dark grey under normal cross-polarised light at all stage angles. If you are far from looking down an optic axis, a flash figure may be seen - a higher order birefringence colour, interrupted four times as the stage is rotated through 360 degrees by "flashes" of black which sweep across the field of view.
An interference figure produced looking straight down or close to the optic axis of a uniaxial mineral will show a characteristic "Maltese" cross shape to its isogyres. If you are looking down the optic axis, the pattern will remain unchanging as the stage is rotated. However, if the viewing angle is away from the optic axis, the centre of the cross will revolve/orbit around the central point as the stage is rotated; the form of the cross will stay constant. The optic axis figure of a biaxial mineral is more complex. One or two curved isogyres will be visible, one of which will have its point of maximum curvature centred. If two isogyres are visible, they will be positioned back-to-back. Rotating the stage will cause the isogyres to move and change shape strikingly - moving from a position where the isogyres curve smoothly and are separated at their closest point gradually becoming more curved/squarer at their midpoints as they approach each other merging to form a maltese cross pattern much like that of a uniaxial mineral.
Continuing to rotate the stage will cause the isogyres to separate again - but into the opposite quadrants to where they were - meet again separate again into their original quadrants, so on. The isogyres will touch each other four times in one 360 degree revolution, with each time corresponding to one of the extinction positions seen in normal cross polarised light; the maximum separation between isogyres occurs when the slide is rotated 45 degrees from one of the orientations where the isogyres come together. The point where the isogyres is most curved represents the position of each of the two optic axes present for a biaxial mineral, thus the maximum separation between the two curves is diagnostic of the angle between the two optic axes for the mineral; this angle is called the optic angle and notated as "2V". In some cases, knowing the optic angle can be a useful diagnostic tool to discriminate between two minerals which otherwise look similar. In other cases, 2V varies with chemical composition in a known way for a given mine
Sandstone is a clastic sedimentary rock composed of sand-sized mineral particles or rock fragments. Most sandstone is composed of quartz or feldspar because they are the most resistant minerals to weathering processes at the Earth's surface, as seen in Bowen's reaction series. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, yellow, grey, pink and black. Since sandstone beds form visible cliffs and other topographic features, certain colors of sandstone have been identified with certain regions. Rock formations that are composed of sandstone allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are better able to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity. Quartz-bearing sandstone can be changed into quartzite through metamorphism related to tectonic compression within orogenic belts.
Sandstones are clastic in origin. They are formed from cemented grains that may either be fragments of a pre-existing rock or be mono-minerallic crystals; the cements binding these grains together are calcite and silica. Grain sizes in sands are defined within the range of 0.0625 mm to 2 mm. Clays and sediments with smaller grain sizes not visible with the naked eye, including siltstones and shales, are called argillaceous sediments; the formation of sandstone involves two principal stages. First, a layer or layers of sand accumulates as the result of sedimentation, either from water or from air. Sedimentation occurs by the sand settling out from suspension. Once it has accumulated, the sand becomes sandstone when it is compacted by the pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains; the most common cementing materials are silica and calcium carbonate, which are derived either from dissolution or from alteration of the sand after it was buried.
Colors will be tan or yellow. A predominant additional colourant in the southwestern United States is iron oxide, which imparts reddish tints ranging from pink to dark red, with additional manganese imparting a purplish hue. Red sandstones are seen in the Southwest and West of Britain, as well as central Europe and Mongolia; the regularity of the latter favours use as a source for masonry, either as a primary building material or as a facing stone, over other forms of construction. The environment where it is deposited is crucial in determining the characteristics of the resulting sandstone, which, in finer detail, include its grain size and composition and, in more general detail, include the rock geometry and sedimentary structures. Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following broad groupings: Terrestrial environmentsRivers Alluvial fans Glacial outwash Lakes Deserts Marine environmentsDeltas Beach and shoreface sands Tidal flats Offshore bars and sand waves Storm deposits Turbidites Framework grains are sand-sized detrital fragments that make up the bulk of a sandstone.
These grains can be classified into several different categories based on their mineral composition: Quartz framework grains are the dominant minerals in most clastic sedimentary rocks. These physical properties allow the quartz grains to survive multiple recycling events, while allowing the grains to display some degree of rounding. Quartz grains evolve from plutonic rock, which are felsic in origin and from older sandstones that have been recycled. Feldspathic framework grains are the second most abundant mineral in sandstones. Feldspar can be divided into two smaller subdivisions: plagioclase feldspars; the different types of feldspar can be distinguished under a petrographic microscope. Below is a description of the different types of feldspar. Alkali feldspar is a group of minerals in which the chemical composition of the mineral can range from KAlSi3O8 to NaAlSi3O8, this represents a complete solid solution. Plagioclase feldspar is a complex group of solid solution minerals that range in composition from NaAlSi3O8 to CaAl2Si2O8.
Lithic framework grains are pieces of ancient source rock that have yet to weather away to individual mineral grains, called lithic fragments or clasts. Lithic fragments can be any fine-grained or coarse-grained igneous, metamorphic, or sedimentary rock, although the most common lithic fragments found in sedimentary rocks are clasts of volcanic rocks. Accessory minerals are all other mineral grains in a sandstone. Common accessory minerals include micas, olivine and corundum. Many of these accessory grains are more dense than the silicates that
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite". Other polymorphs of calcium carbonate are the minerals vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, vaterite is less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime, calx with the suffix -ite used to name minerals, it is thus etymologically related to 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. In publications, two different sets of Miller indices are used to describe directions in calcite crystals - the hexagonal system with three indices h, k, l and the rhombohedral system with four indices h, k, l, i. To add to the complications, there are two definitions of unit cell for calcite.
One, an older "morphological" unit cell, was inferred by measuring angles between faces of crystals and looking for the smallest numbers that fit. A "structural" unit cell was determined using X-ray crystallography; the morphological unit cell has approximate dimensions a = 10 Å and c = 8.5 Å, while for the structural unit cell they are 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, the cleavage is given as "perfect on " in morphological coordinates and "perfect on " in structural units. Twinning and crystal forms are always given in morphological units. Over 800 forms of calcite crystals have been identified. Most common are scalenohedra, with faces in the hexagonal directions or directions. Habits include acute to tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms, it may occur as fibrous, lamellar, or compact. A fibrous, efflorescent form is known as lublinite.
Cleavage is in three directions parallel to the rhombohedron form. Its fracture is difficult to obtain. Scalenohedral faces are chiral and come in pairs with mirror-image symmetry. Rhombohedral faces are achiral, it has a defining Mohs hardness of 3, a specific gravity of 2.71, its luster is vitreous in crystallized varieties. Color is white or none, though shades of gray, orange, green, violet, brown, or black can occur when the mineral is charged with impurities. Calcite is transparent to opaque and may show phosphorescence or fluorescence. A transparent variety called. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the rhombohedral form is sometimes referred to as "nailhead spar". Single calcite crystals display; this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669. At a wavelength of ≈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 between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, dissolved ion concentrations. Although calcite is insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. When conditions are right for dissolution, the removal of calcite can increase the porosity and permeability of the rock, if it continues for a long period of time may result in the formation of caves.
On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, resulting in various forms of karst topography. Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast, whose name contributed to the term alabaster because of the close association. Many other cultures have used the material for similar carved applications. High-grade optical calcite was used in World War II for gun sights in bomb sights and anti-aircraft weaponry. 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. Calcite, obtained from an 80 kg sample of Carrara marble, is used as the IAEA-603 isotopic standard in mass spectrometry for the calibration of δ18O and δ13C. Calcite is a common constituent
Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series; this was first shown by the German mineralogist Johann Friedrich Christian Hessel in 1826. The series ranges from albite to anorthite endmembers, where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is identified by its polysynthetic crystal twinning or'record-groove' effect. Plagioclase is a major constituent mineral in the Earth's crust, is an important diagnostic tool in petrology for identifying the composition and evolution of igneous rocks. Plagioclase is a major constituent of rock in the highlands of the Earth's moon. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars.
The composition of a plagioclase feldspar is denoted by its overall fraction of anorthite or albite, determined by measuring the plagioclase crystal's refractive index in crushed grain mounts, or its extinction angle in thin section under a polarizing microscope. The extinction angle varies with the albite fraction. There are several named plagioclase feldspars that fall between anorthite in the series; the following table shows their compositions in terms of constituent anorthite and albite percentages. Anorthite was named by Gustav Rose in 1823 from the Ancient Greek meaning oblique, referring to its triclinic crystallization. Anorthite is a comparatively rare mineral but occurs in the basic plutonic rocks of some orogenic calc-alkaline suites. Albite is named from the Latin albus, in reference to its unusually pure white color, it is a common and important rock-making mineral associated with the more acid rock types and in pegmatite dikes with rarer minerals like tourmaline and beryl. The intermediate members of the plagioclase group are similar to each other and cannot be distinguished except by their optical properties.
The specific gravity in each member increases 0.02 per 10% increase in anorthite. Bytownite, named after the former name for Ottawa, Canada, is a rare mineral found in more basic rocks. Labradorite is the characteristic feldspar of the more basic rock types such as diorite, andesite, or basalt and is associated with one of the pyroxenes or amphiboles. Labradorite shows an iridescent display of colors due to light refracting within the lamellae of the crystal, it is named after Labrador, where it is a constituent of the intrusive igneous rock anorthosite, composed entirely of plagioclase. A variety of labradorite known as spectrolite is found in Finland. Andesine is a characteristic mineral of rocks such as diorite which contain a moderate amount of silica and related volcanics such as andesite. Oligoclase is common in granite, syenite and gneiss, it is a frequent associate of orthoclase. The name oligoclase is derived from the Greek for little and fracture, in reference to the fact that its cleavage angle differs from 90°.
Sunstone is oligoclase with flakes of hematite. Hypersolvus List of minerals Subsolvus
Canada balsam called Canada turpentine or balsam of fir, is a turpentine made from the resin of the balsam fir tree of boreal North America. The resin, dissolved in essential oils, is a viscous, colourless or yellowish liquid that turns to a transparent yellowish mass when the essential oils have been allowed to evaporate. Canada balsam is amorphous. Since it does not crystallize with age, its optical properties do not deteriorate. However, it has poor solvent resistance. Due to its high optical quality and the similarity of its refractive index to that of crown glass and filtered Canada balsam was traditionally used in optics as an invisible-when-dry glue for glass, such as lens elements. Lenses glued with Canada balsam are called cemented lenses. Other optical elements can be cemented with Canada balsam, such as two prisms bonded to form a beam splitter. Balsam was phased out as an optical adhesive during World War II, in favour of polyester and urethane-based adhesives. In modern optical manufacturing, UV-cured epoxies are used to bond lens elements.
Canada balsam was commonly used for making permanent microscope slides. From about 1830 molten Canada balsam was used for microscope slides Canada balsam in solution was introduced in 1843, becoming popular in the 1850s. In biology, for example, it can be used to conserve microscopic samples by sandwiching the sample between a microscope slide and a glass coverslip, using Canada balsam to glue the arrangement together and enclose the sample to conserve it. Xylene balsam, Canada balsam dissolved in xylene, is used for preparing slide mounts; some workers prefer terpene resin for slide mounts, as it is both less acidic and cheaper than balsam. Synthetic resins have replaced organic balsams for such applications. Another important application of Canada balsam is in the construction of the Nicol prism. A Nicol prism consists of a calcite crystal cut into two halves. Canada balsam is placed between the two layers. Calcite is an anisotropic crystal and has different refractive indices for rays polarized along directions parallel and perpendicular to its optic axis.
These rays with differing refractive indices are known as the extraordinary rays. The refractive index for Canada balsam is in between the refractive index for the ordinary and extraordinary rays. Hence the ordinary ray will be internally reflected; the emergent ray will be linearly polarized, traditionally this has been one of the popular ways of producing polarized light. Some other uses include: in geology, it is used as a common thin section cement and glue and for refractive-index studies and tests, such as the Becke line test. Balm of Gilead, a healing compound made from the resinous gum of Commiphora gileadensis