Yakut: Revizyonlar arasındaki fark
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61. satır:
Temiz bir yakut'un karatı 6000 dolar civarındadır. Nadir bulunduğundan ve sertliği sayesinde çok aranan taştır.
==Physical properties==
[[Image:Corundum.png|thumb|left|Crystal structure of 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 and moissonite falling somewhere in between corundum (ruby) and diamond in hardness. Ruby is α-alumina (the most stable form of Al<sub>2</sub>O<sub>3</sub>) in which a small fraction of the aluminium<sup>3+</sup> ions are replaced by chromium<sup>3+</sup> ions. Each Cr<sup>3+</sup> is surrounded octahedrally by six O<sup>2−</sup> ions. This crystallographic arrangement strongly affects each Cr<sup>3+</sup>, resulting in light absorption in the yellow-green region of the spectrum and thus in the red color of the gem. When yellow-green light is absorbed by Cr<sup>3+</sup>, it is re-emitted as red [[Photoluminescence|luminescence]].<ref>{{cite web| url = http://www.webexhibits.org/causesofcolor/6AA.html| title = Ruby: causes of color| accessdate=15 May 2009}}</ref> This red emission adds to the red color perceived by the subtraction of green and violet light from white light, and adds luster to the gem's appearance. When the optical arrangement is such that the emission is stimulated by 694-nanometer photons reflecting back and forth between two mirrors, the emission grows strongly in intensity. This effect was used by [[Theodore Maiman]] in 1960 to make the first successful [[Ruby laser|laser]], based on ruby.
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, simulants, or substitutes. Usually the rough stone is heated before cutting. Almost all rubies today are treated in some form, with heat treatment being the most common practice. However, rubies that are completely untreated but still of excellent quality command a large premium.
Some rubies show a three-point or six-point [[asterism (gemmology)|asterism]] or "star". These rubies are cut into [[cabochons]] to display the effect properly. Asterisms are best visible with a single-light 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" (the structurally oriented [[rutile]] needle inclusions) in a certain way. This is one example where inclusions increase the value of a gemstone. Furthermore, rubies can show color changes—though this occurs very rarely—as well as [[chatoyancy]] or the "cat's eye" effect.
{{mineral-taslak}}
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