Pleochroism
As light emerges from a doubly refracting transparent stone, the beam is split into two polarised light rays, each vibrating in planes at right angles to each other.
Pleochroism in gemstones
By:Yuman Hussain
Summary: Scientific explanation of Pleochroism which is an ability of the stone to absorb different wavelengths of light displaying brilliant colors when viewed from different directions.
pleochroism
When light passes through a doubly refractive gemstone, the light is split into two rays which are polarized at right angles to each other and travel at differing velocities through the gemstone.
Pleochroism
Pleochroism is the property of having more than two colors, especially when viewed from different angles.
Pleochroism:
Light that passes through a doubly refractive gemstone or anisotropic mineral is split in different directions with varying velocity.
Pleochroism: The ability of certain gems to display two or more colors when viewed from different angles.
Pleochroism: Variation in absorption with direction in doubly refractive colored stones. Uniaxial crystals can potentially show two colors, while biaxial crystals may show up to three colors.
Pleochroism
Change of colors observed in double-refractive gemstones when viewed different directions. Selective absorption and varying transmission rates of light cause the color change when the gemstone is viewed along different optical axes.
Pleochroism
Strongly trichroic: greenish, reddish and yellowish
Phenomena ...
Pleochroism - In a doubly refractive crystal, a light beam reflects two different rays. The eye cannot normally see both rays at the same time, but by moving the stone, the eye will observe both rays. The result?
Pleochroism will not be observed in SR gems, nor in DR gems when looking through an optic axis direction.
Pleochroism may have been helpful in navigation but it makes things difficult for a gem cutter. If iolite is not cut from exactly the right direction, no matter the shape of the rough, its color will not show to its best advantage.
Pleochroism makes it difficult for a gem cutter to orient the stone to get only the blue color.
If iolite is not cut from exactly the right direction, its color will not show to its best advantage.
Chanthaburi ...
Pleochroism
Blue stones - strong, blue and yellow to colorless. Other colors are weak to very weak.[1]
Ultraviolet fluorescence ...
Pleochroism is the apparent change in color of a doubly refractive gemstone when viewed through different directions of the crystal structure.
PLEOCHROISM: The property of most doubly refractive colored gemstones of exhibiting either two or more different colors when observed through a dichroscope in transmitted light.
RAHU: The Moon's ascending (North) node.
RASI: Zodiac sign.
Pleochroism
Usually strong trichroic in reddish-brown, yellow-brown, olive green, yellow, & colorless; In Luning, Nevada material: reddish-brown, deep brown, pale brown, or colorless; In Sri Lankan material: reddish brown, deep violet, & ...
Pleochroism...Dichroism and similar effects shown by some biaxial minerals in which three distinct colors or shades can be seen by using a dichroscope. (two at a time)
Plutonic rock...rock that has solidified deep underground.
pleochroism The effect present in a mineral exhibiting two or more separate colors when viewed at different angles. Pleochroism and dichroism are synonymous, except dichroism refers only to two colors, but pleochroism can be more than two.
It exhibits pleochroism which ranges from light to dark blue. It is a form of plancheite.
The stone has a very pronounced pleochroism (different colors at different angles) and can be seen as dark blue, green-yellow and red-purple. Blue tanzanite is more desirable than purple.
Pleochroism (color changes visible depending on the direction of the light) is very strongly evident in Iolite, and because of this quality, it has been said to be used by the seafaring Vikings for navigation even under cloudy skies.
Many Tourmalines exhibit pleochroism, the variation of colors visible in different axial directions of the crystal.
Generally, while cutting pleochoric stones, the techniques are to reduce the effect of pleochroism and give prominence to the best color.
Most cutters try to minimize pleochroism in gemstones such as iolite and tanzanite by attempting to highlight the single best color.
Pleochroism: weak to none, except in pink stones. Some yellow varieties may show a weak yellow to pink dichroism.
Color: see above.
U.V. Fluorescence: weak; blue and colorless topaz may show a weak yellow or greenish glow under long wavelength u.v..
Has strong pleochroism, meaning the gemstone changes colors depending which angle it is viewed from. Cordierite displays colors ranging from deep blue, to violet and light blue and grayish blue.
Spodumene is known for its strong pleochroism, showing lighter and more intense coloring when viewed at different angles.
Madagascar garnets display
a higher degree of ‘pleochroism' - the tendency to change color in different
lights - than alexandrite, which are known for their color change properties.
Garnet care ...
Gem kunzite is a rose-violet color with strong pleochroism. It is vital that the rough be cut with the correct crystal orientation or the finished gem could be colorless. Kunzite is subject to fading when exposed to strong light.
Alexandrite crystals have an optical property called pleochroism, which means that they are light sensitive and appear to change colour when viewed from different angles and in different types of light.
It has a lower RI than Tanzanite and does not have the same pleochroism so is easily distinguished from the real thing.
(There is a display of fluorescent mineral on the first floor of the (old)Geology Building.) Other optical properties such as index of refraction and pleochroism (differential light absorption) require an optical microscope to measure and are the ...
named for its locality, Tanzanite (from Tanzania) where the only transparent gem variety is found. Thulite is named after Thule, an archaic name for Norway. (strong pleochroism from blue-violet to violet)
Gem info: ...
Physical Properties of Gemstones
The Crystallography and Forms of Gemstones
Types of Gemstone Deposits
Sources of Gemstones
Doublets, Coated Stones And Foilback
Identification By Double Refraction & Pleochroism ...
Ranging from violet to lilac in hue, it is the second most valuable blue gemstone after sapphire. In order to bring out the full beauty of its blueness, tanzanite is often heat-treated. Some tanzanite display pleochroism.
Optics: Isotropic, index very constant: N = 2.417
Dispersion: 0.044. This high dispersion creates the prismatic "fire" responsible for much of a diamond's historic beauty.
Pleochroism: None ...
upon which crystallographic axis is transmitting the light. Such species may demonstrate several different colors as light is transmitted along various different axes. This phenomena of directionally selective absorption is termed pleochroism.
 See also: Color, Crystal, Gemstone, Gemstones, Stone
  
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