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 picture info 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 Silicon dioxide">SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. 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 [...More...] picture info German Language German ( German language text">Deutsch, pronounced International Phonetic Alphabet (IPA)" class="IPA">[dɔʏtʃ] ()) is a West Germanic language that is mainly spoken in Central Europe. It is the most widely spoken and official or co-official language in Germany, Austria, Switzerland, South Tyrol in Italy, the German-speaking Community of Belgium"> German-speaking Community of Belgium and Liechtenstein. It is one of the three official languages of Luxembourg and a co-official language in the Opole Voivodeship in Poland [...More...] picture info Cleavage (crystal) Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes [...More...] Chiral 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 [...More...] picture info Feldspar Feldspars (LiAlSi3O8 – NaAlSi3O8 – Ca [...More...] picture info 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---> [...More...] picture info 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) as well as its heavier analogues. The perfectly symmetrical tetrahedron belongs to point group Td, but most tetrahedral molecules have lower symmetry [...More...] picture info Racemic Mixture In chemistry, a racemic mixture, or racemate /reɪˈsimeɪt/, is one that has equal amounts of left- and right-handed enantiomers of a Chirality (chemistry)">chiral molecule. The first known racemic mixture was Racemic acid">racemic acid, which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid [...More...] 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 [...More...] picture info 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 presence of other chemicals (including changes to 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. Insolubility is the inability to dissolve in a solid, liquid or gaseous solvent. Most often, the solvent is a liquid, which can be a pure substance or a mixture [...More...] picture info 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 [...More...] picture info Pleochroism Pleochroism (from Greek πλέων, pléōn, "more" and χρῶμα, khrôma, "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. [...More...] picture info 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 (molecule)">water at its densest (at 4 °C or 39.2 °F); for gases it is air at room temperature (20 °C or 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 fuel Temperatures for both sample and reference vary from industry to industry [...More...] picture info 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 ${\displaystyle n={\frac {c}{v}},}$ 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 of a light ray The refractive index determines how much the path of light is bent, or refracted, when entering a material [...More...]