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Possible definitions for quarto
quartz
Second most abundant mineral (after feldspar) in the earth's crust, present in many rocks. Quartz, which consists of silica, or silicon dioxide (SiO2), has great economic importance. Many varieties are gemstones, incl. amethyst, citrine, smoky quartz, and rose quartz. Sandstone, composed mainly of quartz, is an important building stone. Large amounts of quartz sand (or silica sand) are used in the manufacture of glass and ceramics and for molds in metal casting. Crushed quartz is used as an abrasive in sandpaper; silica sand is employed in sandblasting; and sandstone is used whole to make whetstones, millstones, and grindstones. Silica glass (or fused quartz) is used in optics to transmit ultraviolet light. Tubing and various vessels of fused quartz have important laboratory applications, and quartz fibers are employed in extremely sensitive weighing devices.
equator
Great circle around the earth that is everywhere equidistant from the geographic poles and lies in a plane perpendicular to the earth's axis. This geographic, or terrestrial, equator divides the earth into the Northern and Southern Hemispheres and forms the imaginary reference line on the earth's surface from which latitude is reckoned (i.e., 0° latitude). In astronomy, the celestial equator is the great circle in which the plane of the terrestrial equator intersects the celestial sphere; it is thus equidistant from the celestial poles. When the sun lies in its plane, day and night are everywhere of equal length; this happens at the equinoxes.
Khartoum
City (pop., 1993: 925,000), capital of the Sudan. Located just south of the confluence of the Blue and White Nile rivers, it was originally an Egyptian army camp (1821). The Mahdists besieged and destroyed the town in 1885, killing C. G. Gordon, the British governor-general. Reoccupied by the British in 1898, it served as the seat of the Anglo-Egyptian government until 1956, when it became the capital of the independent republic of the Sudan. A major trade and communications center, it is the seat of several universities.
quantum
In physics, a discrete natural unit, or packet, of energy, charge, angular momentum, or other physical property. Light, for example, which appears in some respects as a continuous electromagnetic wave, on the submicroscopic level is emitted and absorbed in discrete amounts, or quanta; for light of a given wavelength, the magnitude of all the quanta emitted or absorbed is the same in both energy and momentum. These particlelike packets of light are called photons, a term also applicable to quanta of other forms of electromagnetic energy such as X rays and gamma rays. Submicroscopic mechanical vibrations in the layers of atoms comprising crystals also give up or take on energy and momentum in quanta called phonons. See also quantum mechanics.
quark
Any of a group of subatomic particles thought to be among the ...
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