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Quartz
Quartz
Quartz
is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz
Quartz
is the second most abundant mineral in Earth's continental crust, behind feldspar.[7] Quartz
Quartz
crystals are chiral, and exist in two forms, the normal α-quartz and the high-temperature β-quartz. The transformation from α-quartz to β-quartz takes place abruptly at 573 °C (846 K). Since the transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit. There are many different varieties of quartz, several of which are semi-precious gemstones
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German Language
No official regulation ( German orthography
German orthography
regulated by the Council for German Orthography[4]). Language
Language
codesISO 639-1 deISO 639-2 ger (B) deu (T)ISO 639-3 Variously: deu – German gmh&#
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Cleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye.[1]Contents1 Types of cleavage 2 Parting 3 Uses 4 See also 5 ReferencesTypes of cleavage[edit] Miller indices
Miller indices
h k ℓ Cleavage forms parallel to crystallographic planes:[1]Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Graphite
Graphite
has basal cleavage. Mica
Mica
(like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets. Cubic cleavage occurs on when there are three cleavage planes intersecting at 90 degrees
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Chiral
Chirality
Chirality
/kaɪˈrælɪtiː/ is a property of asymmetry important in several branches of science. The word chirality is derived from the Greek χειρ (kheir), "hand," a familiar chiral object. An object or a system is chiral if it is distinguishable from its mirror image; that is, it cannot be superposed onto it. Conversely, a mirror image of an achiral object, such as a sphere, cannot be distinguished from the object. A chiral object and its mirror image are called enantiomorphs (Greek, "opposite forms") or, when referring to molecules, enantiomers. A non-chiral object is called achiral (sometimes also amphichiral) and can be superposed on its mirror image
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Feldspar
Feldspars (LiAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight.[2] Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock.[3] Rock formed almost entirely of calcic plagioclase feldspar (see below) is known as anorthosite.[4] Feldspars are also found in many types of sedimentary rocks.[5]Contents1 Etymology 2 Compositions2.1 Alkali feldspars 2.2 Barium
Barium
feldspars 2.3
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Continental Crust
Continental crust
Continental crust
is the layer of igneous, sedimentary, and metamorphic rocks that forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is more felsic compared to the oceanic crust, called sima which has a more mafic bulk composition. Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character. The continental crust consists of various layers, with a bulk composition that is intermediate to felsic. The average density of continental crust is about 2.7 g/cm3, less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm3
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Tetrahedral Molecular Geometry
In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1(−⅓) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane (CH4)[1][2] as well as its heavier analogues. The perfectly symmetrical tetrahedron belongs to point group Td, but most tetrahedral molecules have lower symmetry. Tetrahedral molecules can be chiral.Contents1 Examples1.1 Main group chemistry 1.2 Transition metal chemistry 1.3 Water structure2 Bitetrahedral structures 3 Exceptions and distortions3.1 Inverted tetrahedral geometry 3.2 Planarization 3.3 Tetrahedral molecules with no central atom4 See also 5 References 6 External linksExamples[edit] Main group chemistry[edit]The tetrahedral molecule methane (CH4)Aside from virtually all saturated organic compounds, most compounds of Si, Ge, and Sn are tetrahedral
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Racemic Mixture
In chemistry, a racemic mixture, or racemate /reɪˈsimeɪt/, is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was racemic acid, which Louis Pasteur
Louis Pasteur
found to be a mixture of the two enantiomeric isomers of tartaric acid. A sample with only a single enantiomer is an enantiomerically pure, enantiopure or homochiral compound.[1]Contents1 Etymology 2 Nomenclature 3 Properties 4 Crystallization 5 Resolution 6 Synthesis 7 Racemic
Racemic
pharmaceuticals 8 Wallach's rule 9 See also 10 ReferencesEtymology[edit] From racemic acid found in grapes; from Latin racemus, meaning a bunch of grapes. Nomenclature[edit] A racemic mixture is denoted by the prefix (±)- or dl- (for sugars the prefix dl- may be used), indicating an equal (1:1) mixture of dextro and levo isomers
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Standard Conditions For Temperature And Pressure
Standard conditions for temperature and pressure are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted standards
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Solubility
Solubility
Solubility
is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and the pH of the solution. The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute. Most often, the solvent is a liquid, which can be a pure substance or a mixture
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Melting Point
The melting point (or, rarely, liquefaction point) of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance
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Pleochroism
Pleochroism
Pleochroism
(from Greek πλέων, pléōn, "more" and χρῶμα, khrôma, "colour") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light.[1]Contents1 Background 2 In mineralogy and gemology 3 List of pleochroic minerals3.1 Purple and violet 3.2 Blue 3.3 Green 3.4 Yellow 3.5 Brown and orange 3.6 Red and pink4 See also 5 ReferencesBackground[edit] Anisotropic crystals will have optical properties that vary with the direction of light. The direction of the electric field determines the polarization of light, and crystals will respond in different ways if this angle is changed. These kinds of crystals have one or two optical axes
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Specific Gravity
Specific gravity
Specific gravity
is the ratio of the density of a substance to the density of a reference substance; equivalently, it is the ratio of the mass of a substance to the mass of a reference substance for the same given volume. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance for liquids is nearly always water at its densest (at 4 °C / 39.2 °F); for gases it is air at room temperature (20°C / 68° F). Nonetheless, the temperature and pressure must be specified for both the sample and the reference. Pressure is nearly always 1 atm (101.325 kPa).A US Navy Aviation Boatswain's Mate tests the specific gravity of JP-5 fuelTemperatures for both sample and reference vary from industry to industry
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Streak (mineralogy)
The streak (also called "powder color") of a mineral is the color of the powder produced when it is dragged across an un-weathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus an important diagnostic tool in mineral identification. If no streak seems to be made, the mineral's streak is said to be white or colorless. Streak is particularly important as a diagnostic for opaque and colored materials. It is less useful for silicate minerals, most of which have a white streak or are too hard to powder easily. The apparent color of a mineral can vary widely because of trace impurities or a disturbed macroscopic crystal structure. Small amounts of an impurity that strongly absorbs a particular wavelength can radically change the wavelengths of light that are reflected by the specimen, and thus change the apparent color
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Tenacity (mineralogy)
In mineralogy, tenacity is a mineral's behavior when deformed or broken. Common terms[1][edit] Brittleness: The mineral breaks or powders easily. Most ionic-bonded minerals are brittle. Malleability: The mineral may be pounded out into thin sheets. Metallic-bonded minerals are usually malleable. Ductility: The mineral may be drawn into a wire. Ductile materials have to be malleable as well as tough. Sectility: May be cut smoothly with a knife. Relatively few minerals are sectile. Sectility is a form of tenacity and can be used to distinguish minerals of similar appearance.[2] Gold, for example, is sectile but pyrite ("fool's gold") is not. Elasticity: If bent, will spring back to its original position when the stress is released. Plasticity: If bent, will not spring back to its original position when the stress is released. It stays bent
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Refractive Index
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium. It is defined as n = c v , displaystyle n= frac c v , where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in vacuum than in the water. Refraction
Refraction
of a light rayThe refractive index determines how much the path of light is bent, or refracted, when entering a material. This is the first documented use of refractive indices and is described by Snell's law
Snell's law
of refraction, n1 sinθ1 = n2 sinθ2, where θ1 and θ2 are the angles of incidence and refraction, respectively, of a ray crossing the interface between two media with refractive indices n1 and n2
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