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The Alexandrite effect has also been observed in some other minerals, such as fluorite, sapphire, kyanite, monazite, spinel, garnet, tourmaline, and rare-earth oxalates. Not to be confused with the alexandrite effect, some minerals also exhibit pleochroism. The former is a response to different wavelengths of light in general, the latter an ...
Tetragonal, trigonal, and hexagonal minerals can only show two colors and are called dichroic. Orthorhombic , monoclinic , and triclinic crystals can show three and are trichroic. For example, hypersthene , which has two optical axes, can have a red, yellow, or blue appearance when oriented in three different ways in three-dimensional space. [ 5 ]
Stones that show a dramatic color change and strong colors (e.g., red-to-green) are rare and sought-after, [8] but stones that show less distinct colors (e.g. yellowish green changing to brownish yellow) may also be considered "alexandrite" by gem labs such as the Gemological Institute of America. [13] [14]
Synthetic alexandrite is an artificially grown crystalline variety of chrysoberyl, composed of beryllium aluminum oxide (BeAl 2 O 4). The name is also often used erroneously to describe synthetically-grown corundum that simulates the appearance of alexandrite , but with a different mineral composition.
Hydroquinone-induced exogenous ochronosis is an avoidable dermatosis that is exceedingly difficult to treat. However, some studies show that treatment may be possible with a Q-switched alexandrite (755 nm) laser. [13] Individuals with this disorder are recommended to stop using hydroquinone-containing compounds. [2]
The Helmholtz–Kohlrausch effect (after Hermann von Helmholtz and V. A. Kohlrausch [1]) is a perceptual phenomenon where some hues, even when of the same lightness, appear to be bolder than others. Each color on top has approximately the same luminance level and yet they do not appear equally bright or dark.
Hardy's paradox is a thought experiment in quantum mechanics devised by Lucien Hardy [1] [2] in 1992–1993 in which a particle and its antiparticle may interact without annihilating each other.
A crisp parhelic circle (horizontal line) over South Pole Station. Photo: John Bortniak, NOAA, January 1979. A halo display observed over the South Pole. Featured in the photo are several distinct phenomena: A parhelic circle (horizontal line), a 22° halo (circle) with two sundogs (bright spots), and an upper tangent arc.