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2. Pleochroism - Wikipedia

   en.wikipedia.org/wiki/Pleochroism

   Pleochroism is an extremely useful tool in mineralogy and gemology for mineral and gem identification, since the number of colors visible from different angles can identify the possible crystalline structure of a gemstone or mineral and therefore help to classify it. Minerals that are otherwise very similar often have very different pleochroic ...

3. Amethyst - Wikipedia

   en.wikipedia.org/wiki/Amethyst

   Amethyst is a violet variety of quartz.The name comes from the Koine Greek αμέθυστος amethystos from α - a-, "not" and μεθύσκω (Ancient Greek) methysko / μεθώ metho (Modern Greek), "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. [1]

4. Opal - Wikipedia

   en.wikipedia.org/wiki/Opal

   There are two broad classes of opal: precious and common. Precious opal displays play-of-color (iridescence); common opal does not. [5] Play-of-color is defined as "a pseudo chromatic optical effect resulting in flashes of colored light from certain minerals, as they are turned in white light."

5. Dispersion (optics) - Wikipedia

   en.wikipedia.org/wiki/Dispersion_(optics)

   Dispersion is a material property. The amount of fire demonstrated by a given gemstone is a function of the gemstone's facet angles, the polish quality, the lighting environment, the material's refractive index, the saturation of color, and the orientation of the viewer relative to the gemstone. [10] [11]

6. Iridescence - Wikipedia

   en.wikipedia.org/wiki/Iridescence

   Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstructures or thin films .

7. Mineral - Wikipedia

   en.wikipedia.org/wiki/Mineral

   For example, amethyst is a purple variety of the mineral species quartz. Some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure; for example, the formula of mackinawite is given as (Fe,Ni) 9 S 8, meaning Fe x Ni 9-x S 8, where x is a variable number between ...

8. Asterism (gemology) - Wikipedia

   en.wikipedia.org/wiki/Asterism_(gemology)

   A distinction can be made between two types of asterism: Epiasterism, such as that seen in sapphire and most other gems, is the result of a reflection of light on parallel arranged inclusions inside the gemstone. Diasterism, such as that seen in rose quartz, is the result of light transmitted through the stone. In order to see this effect, the ...

9. Metamerism (color) - Wikipedia

   en.wikipedia.org/wiki/Metamerism_(color)

   Color matches made in the paint industry are often aimed at achieving a spectral color match rather than just a tristimulus (metameric) color match under a given spectrum of light. A spectral color match attempts to give two colors the same spectral reflectance characteristic, making them a good metameric match with a low degree of metamerism ...