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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 ...
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.
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 ]
The London-based Royal Observatory Greenwich was able to observe a large sunspot on January 15 due to a short break in the cloud cover. The latitude of the sunspot was on the +19° N declination on the sun's hemisphere, and the sunspot at its maximum size covered an area of roughly 3,000 Millionths of the Solar Hemisphere, or 3,000(MSH).
Initial research at one location identified a longer period experienced by black dogs before adoption, but subsequent studies considered to be more robust (as conducted in a larger number of geographically spread shelters) have shown that when shelter visitors video-recorded their walk through the adoption area, they spent equal amounts of time looking at every dog, regardless of coat color. [4]
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.
The Library was one of the largest and most significant libraries of the ancient world, but details about it are a mixture of history and legend. [17] The earliest known surviving source of information on the founding of the Library of Alexandria is the pseudepigraphic Letter of Aristeas , which was composed between c. 180 and c. 145 BC.