In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure.
The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof.
That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
Mohs scale of mineral hardness
The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, while greatly facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Despite its lack of precision, the Mohs scale is highly relevant for field geologists, the Mohs scale hardness of minerals can be commonly found in reference sheets. Reference materials may be expected to have a uniform Mohs hardness, the Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. The samples of matter used by Mohs are all different minerals, Minerals are pure substances found in nature. Rocks are made up of one or more minerals, as the hardest known naturally occurring substance when the scale was designed, diamonds are at the top of the scale.
The hardness of a material is measured against the scale by finding the hardest material that the material can scratch. For example, if material is scratched by apatite but not by fluorite. Scratching a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye, materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number. The Mohs scale is an ordinal scale. For example, corundum is twice as hard as topaz, the table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples. On the Mohs scale, a streak plate has a hardness of 7.0, using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. The table below incorporates additional substances that may fall between levels, Comparison between Hardness and Hardness, Mohs hardness of elements is taken from G. V, samsonov in Handbook of the physicochemical properties of the elements, IFI-Plenum, New York, USA,1968.
The Hardness of Minerals and Rocks
A loupe is a simple, small magnification device used to see small details more closely. Loupes are called hand lenses, three basic types of loupes exist, Simple lenses, generally used for low-magnification designs because of high optical aberration. Compound lenses, generally used for higher magnifications to control optical aberration, loupes are used in a number of industries, notably the jewelry trade, photography, dentistry and ophthalmology. Loupes are used in academia and life sciences, such as geology and biology, amateur naturalists may find a hand lens or a loupe a useful tool when looking at or identifying species. They are used in numismatics and stamp collecting, jewelers typically use a monocular, handheld loupe in order to magnify gemstones and other jewelry that they wish to inspect. A 10× magnification is good to use for inspecting jewelry and hallmarks and is the Gemological Institute of Americas standard for grading diamond clarity. Stones will sometimes be inspected at higher magnifications than 10×, although the depth of field, the accepted standard for grading diamonds is therefore that inclusions and blemishes visible at 10× impact the clarity grade.
Loupes are employed to assist watchmakers in assembling mechanical watches, typical magnifications for viewing slides full-frame depend on image format,35 mm frames are best viewn at ca. 5×, while ca. 3× is optimal for viewing medium format slides, often, a 10× loupe is used to examine critical sharpness. Photographers using large format cameras use a loupe to view the ground glass image to aid in focusing. DSLR camera users use loupes to help to identify dust and other particles on the sensor and flexographic printing see frequent use of loupes in order to carefully analyze how ink lies on paper. Strippers use loupes in order to register film separations to one another, pressmen use them to check registration of colors, estimate dot-gain, and diagnose issues with roller pressure and chemistry based on the shape of individual dots and rosettes. Dental loupes aid dentists and dental therapists to devise accurate diagnose of oral conditions, loupes can improve dentists posture which can decrease occupational strain.
Dental caries, known as cavities, are most accurately identified by visual and tactile examination of a clean, magnification enables dentists to improve their ability to differentiate between a stain and a cavity. Cavities are rated and scored based on their visual presentation, if magnification is too high diagnosis becomes difficult due to the small field of view. Ideal magnification for diagnostic purposes is up to 2×, treatment of dental caries, periodontal disease, and pulpal disease are aided by magnification. The dental specialty of endodontics has performed the vast majority of research regarding magnification in dentistry, treatment of periodontal disease is achieved by removing calculus deposits and therefore bacteria which causes inflammation and subsequently bone destruction. In severe cases, surgery to reduce pocket depth is indicated and hygienists must visualize plaque and calculus to remove it
Integrated Authority File
The Integrated Authority File or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used mainly for documentation in libraries and increasingly by archives, the GND is managed by the German National Library in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero license, the GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, and an approach to unambiguous identification of single elements. It comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format
In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation. In gemology, an inclusion is a characteristic enclosed within a gemstone, according to Huttons law of inclusions, fragments included in a host rock are older than the host rock itself. Inclusions are usually other minerals or rocks, but may be water, liquid or vapor inclusions are known as fluid inclusions. In the case of amber it is possible to find insects and plants as inclusions, the analysis of atmospheric gas bubbles as inclusions in ice cores is an important tool in the study of climate change. A xenolith is a rock which has been picked up by a lava flow. Melt inclusions form when bits of melt become trapped inside crystals as they form in the melt, inclusions are one of the most important factors when it comes to gem valuation. In many gemstones, such as diamonds, inclusions affect the clarity of the gem, in some gems, such as star sapphires, the inclusion actually increases the value of the gem.
Many colored gemstones, such as amethyst and sapphire, are expected to have inclusions, colored gemstones are categorized into three types as follows, Type I colored gems include gems with very little or no inclusions. They include aquamarines and zircon, Type II colored gems include those that often have a few inclusions. They include sapphire, ruby and spinel, Type III colored gems include those that almost always have inclusions. Gems in this category include emerald and tourmaline, the term inclusion is used in the context of metallurgy and metals processing. During the melt stage of processing hard particles such as oxides can enter or form in the metal which are subsequently trapped when the melt solidifies. The term is used negatively such as when the particle could act as a fatigue crack nucleator or as an area of high stress intensity
Mineralogy is a subject of geology specializing in the scientific study of chemistry, crystal structure, and physical properties of minerals and mineralized artifacts. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, the German Renaissance specialist Georgius Agricola wrote works such as De re metallica and De Natura Fossilium which began the scientific approach to the subject. Systematic scientific studies of minerals and rocks developed in post-Renaissance Europe, the modern study of mineralogy was founded on the principles of crystallography and to the microscopic study of rock sections with the invention of the microscope in the 17th century. Nicholas Steno first observed the law of constancy of interfacial angles in quartz crystals in 1669 and this was generalized and established experimentally by Jean-Baptiste L. Romé de lIslee in 1783. In 1814, Jöns Jacob Berzelius introduced a classification of minerals based on their chemistry rather than their crystal structure, james D.
Dana published his first edition of A System of Mineralogy in 1837, and in a edition introduced a chemical classification that is still the standard. It, retains a focus on the structures commonly encountered in rock-forming minerals. An initial step in identifying a mineral is to examine its physical properties and these can be classified into density, measures of mechanical cohesion, macroscopic visual properties and electric properties and solubility in hydrogen chloride. If the mineral is crystallized, it will have a distinctive crystal habit that reflects the crystal structure or internal arrangement of atoms. It is affected by crystal defects and twinning. Many crystals are polymorphic, having more than one crystal structure depending on factors such as pressure and temperature. ”Examples of polymorphs are calcite and aragonite - two minerals with identical chemical composition, distinguished by their crystallography, calcite is rhombohedral and aragonite is orthorhombic. The crystal structure is the arrangement of atoms in a crystal and it is represented by a lattice of points which repeats a basic pattern, called a unit cell, in three dimensions.
The lattice can be characterized by its symmetries and by the dimensions of the unit cell and these dimensions are represented by three Miller indices. The lattice remains unchanged by certain symmetry operations about any point in the lattice, rotation and rotary inversion. Together, they make up an object called a crystallographic point group or crystal class. There are 32 possible crystal classes, in addition, there are operations that displace all the points, screw axis, and glide plane. In combination with the point symmetries, they form 230 possible space groups, most geology departments have X-ray powder diffraction equipment to analyze the crystal structures of minerals. X-rays have wavelengths that are the order of magnitude as the distances between atoms. In a sample that is ground to a powder, the X-rays sample a random distribution of all crystal orientations, powder diffraction can distinguish between minerals that may appear the same in a hand sample, for example quartz and its polymorphs tridymite and cristobalite
A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum. Other varieties of gem-quality corundum are called sapphires, Ruby is one of the traditional cardinal gems, together with amethyst, sapphire and diamond. They word ruby comes from ruber, Latin for red, the color of a ruby is due to the element chromium. The quality of a ruby is determined by its color and clarity, the brightest and most valuable red called blood-red or pigeon blood, commands a large premium over other rubies of similar quality. After color follows clarity, similar to diamonds, a stone will command a premium. Ruby is the birthstone for July and is usually more pink than garnet. The worlds most expensive ruby is the Sunrise Ruby, rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10.0, when a chromium atom replaces an occasional aluminum atom, it too loses 3 electrons to become a chromium3+ ion to maintain the charge balance of the Al2O3 crystal.
However, the Cr3+ ions are larger and have electron orbitals in different directions than aluminum, the octahedral arrangement of the O2− ions is distorted, and the energy levels of the different orbitals of those Cr3+ ions are slightly altered because of the directions to the O2− ions. Those energy differences correspond to absorption in the ultraviolet, violet, if one percent of the aluminum ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem. Additionally, absorption at any of the above wavelengths stimulates fluorescent emission of 694-nanometer-wavelength red light, after absorbing short-wavelength light, there is short interval of time when the crystal lattice of ruby is in an excited state before fluorescence occurs. If 694-nanometer photons pass through the crystal during that time, they can stimulate more fluorescent photons to be emitted in-phase with them, thus strengthening the intensity of that red light. By arranging mirrors or other means to pass emitted light repeatedly through the crystal, all natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as silk.
Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, usually, the rough stone is heated before cutting. These days, almost all rubies are treated in some form, untreated rubies of high quality command a large premium. Some rubies show a three-point or six-point asterism or star and these rubies are cut into cabochons to display the effect properly. Asterisms are best visible with a source and move across the stone as the light moves or the stone is rotated. Such effects occur when light is reflected off the silk in a certain way and this is one example where inclusions increase the value of a gemstone
Jewellery or jewelry consists of small decorative items worn for personal adornment, such as brooches, necklaces and bracelets. Jewellery may be attached to the body or the clothes, for many centuries metal, often combined with gemstones, has been the normal material for jewellery, but other materials such as shells and other plant materials may be used. It is one of the oldest type of archaeological artefact – with 100, the most widespread influence on jewellery in terms of design and style have come from Asia. Jewellery may be made from a range of materials. Gemstones and similar such as amber and coral, precious metals and shells have been widely used. In most cultures jewellery can be understood as a symbol, for its material properties, its patterns. Jewellery has been made to nearly every body part, from hairpins to toe rings. The word jewellery itself is derived from the jewel, which was anglicised from the Old French jouel. In British English, Indian English, New Zealand English, Hiberno-English, Australian English, both are used in Canadian English, though jewelry prevails by a two to one margin.
Numerous cultures store wedding dowries in the form of jewellery or make jewellery as a means to store or display coins, jewellery has been used as a currency or trade good, an example being the use of slave beads. Many items of jewellery, such as brooches and buckles, originated as functional items. Jewellery can symbolise group membership or status, wearing of amulets and devotional medals to provide protection or ward off evil is common in some cultures. These may take the form of symbols, plants, body parts, in creating jewellery, coins, or other precious items are often used, and they are typically set into precious metals. Alloys of nearly every metal known have been encountered in jewellery, for example, was common in Roman times. Modern fine jewellery usually includes gold, white gold, palladium, most contemporary gold jewellery is made of an alloy of gold, the purity of which is stated in karats, indicated by a number followed by the letter K. American gold jewellery must be of at least 10K purity, many whimsical fashions were introduced in the extravagant eighteenth century.
Cameos that were used in connection with jewellery were the attractive trinkets along with many of the objects such as brooches, ear-rings. Some of the necklets were made of pieces joined with the gold chains were in and bracelets were made sometimes to match the necklet
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe. The formal sciences are often excluded as they do not depend on empirical observations, disciplines which use science, like engineering and medicine, may be considered to be applied sciences. However, during the Islamic Golden Age foundations for the method were laid by Ibn al-Haytham in his Book of Optics. In the 17th and 18th centuries, scientists increasingly sought to formulate knowledge in terms of physical laws, over the course of the 19th century, the word science became increasingly associated with the scientific method itself as a disciplined way to study the natural world. It was during this time that scientific disciplines such as biology, Science in a broad sense existed before the modern era and in many historical civilizations. Modern science is distinct in its approach and successful in its results, Science in its original sense was a word for a type of knowledge rather than a specialized word for the pursuit of such knowledge.
In particular, it was the type of knowledge which people can communicate to each other, for example, knowledge about the working of natural things was gathered long before recorded history and led to the development of complex abstract thought. This is shown by the construction of calendars, techniques for making poisonous plants edible. For this reason, it is claimed these men were the first philosophers in the strict sense and they were mainly speculators or theorists, particularly interested in astronomy. In contrast, trying to use knowledge of nature to imitate nature was seen by scientists as a more appropriate interest for lower class artisans. A clear-cut distinction between formal and empirical science was made by the pre-Socratic philosopher Parmenides, although his work Peri Physeos is a poem, it may be viewed as an epistemological essay on method in natural science. Parmenides ἐὸν may refer to a system or calculus which can describe nature more precisely than natural languages. Physis may be identical to ἐὸν and he criticized the older type of study of physics as too purely speculative and lacking in self-criticism.
He was particularly concerned that some of the early physicists treated nature as if it could be assumed that it had no intelligent order, explaining things merely in terms of motion and matter. The study of things had been the realm of mythology and tradition, however. Aristotle created a less controversial systematic programme of Socratic philosophy which was teleological and he rejected many of the conclusions of earlier scientists. For example, in his physics, the sun goes around the earth, each thing has a formal cause and final cause and a role in the rational cosmic order. Motion and change is described as the actualization of potentials already in things, while the Socratics insisted that philosophy should be used to consider the practical question of the best way to live for a human being, they did not argue for any other types of applied science
Total internal reflection
Total internal reflection is the phenomenon which occurs when a propagated wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the side of the boundary and the incident angle is greater than the critical angle. The critical angle is the angle of incidence above which the internal reflection occurs. This is particularly common as a phenomenon, where light waves are involved. When a wave reaches a boundary between different materials with different refractive indices, the wave will in general be partially refracted at the boundary surface, and partially reflected. This can only occur when the wave in a medium with a refractive index reaches a boundary with a medium of lower refractive index. For example, it will occur with light reaching air from glass, Total internal reflection of light can be demonstrated using a semi-circular block of glass or plastic. A ray box shines a beam of light onto the glass medium.
At the glass/air boundary of the surface, what happens will depend on the angle. If θc is the angle, the following scenarios depict what will happen according to the size of the incident angle. If θ ≤ θc, the ray will split, some of the ray will reflect off the boundary and this is not total internal reflection. If θ > θc, the ray reflects from the boundary. This is called total internal reflection and this physical property makes optical fibers useful and prismatic binoculars possible. It is what gives diamonds their distinctive sparkle, as diamond has a high refractive index. The critical angle is the angle of incidence for which the angle of refraction is 90°, the angle of incidence is measured with respect to the normal at the refractive boundary. Consider a light ray passing from glass into air, the light emanating from the interface is bent towards the glass. When the incident angle is increased sufficiently, the transmitted angle reaches 90 degrees and it is at this point no light is transmitted into air.
The critical angle θ c is given by Snells law, n 1 sin θ i = n 2 sin θ t, rearranging Snells Law, we get incidence sin θ i = n 2 n 1 sin θ t
A refractometer is a laboratory or field device for the measurement of an index of refraction. There are four types of refractometers, traditional handheld refractometers, digital handheld refractometers, laboratory or Abbe refractometers. There is the Rayleigh Refractometer used for measuring the refractive indices of gases, in veterinary medicine, a refractometer is used to measure the total plasma protein in a blood samples. In drug diagnostics, a refractometer is used to measure the gravity of human urine. In gemology/gemmology, the gemstone refractometer is one the fundamental pieces of equipment used in a gemological laboratory, gemstones are transparent minerals and can therefore be examined using optical methods. Refractive index is a constant, dependent on the chemical composition of a substance. The refractometer is used to help identify gem materials by measuring their refractive index, due to the dependence of the refractive index on the wavelength of the light used, the measurement is normally taken at the wavelength of the sodium line D-line of ~589 nm.
This is either filtered out from daylight or generated with a monochromatic light-emitting diode, certain stones such as rubies, sapphires and topaz are optically anisotropic. They demonstrate birefringence based on the plane of the light. The two different refractive indexes are classified using a polarisation filter, Gemstone refractometers are available both as classic optical instruments and as electronic measurement devices with a digital display. In marine aquarium keeping, a refractometer is used to measure the salinity, in the Automobile Industry, a refractometer is used to measure the Coolant Concentration and the Ph Value of the Coolant Oils for the CNC Machining Process. In homebrewing, a refractometer is used to measure the gravity before fermentation to determine the amount of fermentable sugars which will potentially be converted to alcohol. In beekeeping, a refractometer is used to measure the amount of water in honey, automatic refractometers automatically measure the refractive index of a sample.
The automatic measurement of the index of the sample is based on the determination of the critical angle of total reflection. A light source, usually a long-life LED, is focused onto a surface via a lens system. An interference filter guarantees the specified wavelength, due to focusing light to a spot at the prism surface, a wide range of different angles is covered. As shown in the figure Schematic setup of an automatic refractometer the measured sample is in contact with the measuring prism. This dependence of the light intensity from the incident angle is measured with a high-resolution sensor array
An optical spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the lights intensity but could also, for instance, a spectrometer is used in spectroscopy for producing spectral lines and measuring their wavelengths and intensities. Spectrometers may operate over a range of non-optical wavelengths. If the instrument is designed to measure the spectrum in absolute units rather than relative units, the majority of spectrophotometers are used in spectral regions near the visible spectrum. In general, any particular instrument will operate over a portion of this total range because of the different techniques used to measure different portions of the spectrum. Below optical frequencies, the analyzer is a closely related electronic device. Spectrometers are used in many fields, for example, they are used in astronomy to analyze the radiation from astronomical objects and deduce chemical composition.
The spectrometer uses a prism or a grating to spread the light from a distant object into a spectrum and this allows astronomers to detect many of the chemical elements by their characteristic spectral fingerprints. If the object is glowing by itself, it will show spectral lines caused by the gas itself. These lines are named for the elements which cause them, such as the alpha, beta. Chemical compounds may be identified by absorption, typically these are dark bands in specific locations in the spectrum caused by energy being absorbed as light from other objects passes through a gas cloud. Much of our knowledge of the makeup of the universe comes from spectra. Spectroscopes are often used in astronomy and some branches of chemistry, early spectroscopes were simply prisms with graduations marking wavelengths of light. Modern spectroscopes generally use a diffraction grating, a movable slit, Fraunhofer went on to invent the first diffraction spectroscope. Gustav Robert Kirchhoff and Robert Bunsen discovered the application of spectroscopes to chemical analysis and Bunsens analysis enabled a chemical explanation of stellar spectra, including Fraunhofer lines.
When a material is heated to incandescence it emits light that is characteristic of the makeup of the material. Particular light frequencies give rise to sharply defined bands on the scale which can be thought of as fingerprints, in the original spectroscope design in the early 19th century, light entered a slit and a collimating lens transformed the light into a thin beam of parallel rays. The light passed through a prism that refracted the beam into a spectrum because different wavelengths were refracted different amounts due to dispersion and this image was viewed through a tube with a scale that was transposed upon the spectral image, enabling its direct measurement