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Topic: Pleochroism


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  Pleochroism - Wikipedia, the free encyclopedia
Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other.
Gems are sometimes cut and set either to display pleochroism or to hide it, depending on the colors and their attractiveness.
Pleochroism is an extremely useful tool in mineralogy for mineral identification, since minerals that are otherwise very similar often have very different pleochroic color schemes.
en.wikipedia.org /wiki/Pleochroism   (187 words)

  
 Mineral Gallery - Pleochroism, Phosphorescence and other light effects
Pleochroic minerals are minerals that show different colors depending on what direction the viewer is observing the crystal.
Many minerals are technically pleochroic, but more often than not the color change is so small that it requires optical instruments to detect it.
Pleochroism is caused by the absorption of different wavelengths of light travelling through different directions in the crystal.
mineral.galleries.com /minerals/property/pleochro.htm   (1012 words)

  
 Apatite - Victoria
The color effects resembling pleochroism in these cores are regarded as due to the reflection and transmission of light by numerous small included particles, the ranges of pleochroism depending upon the size and arrangement of these particles.
The pleochroic changes are grouped thus: (a) from almost fl, dark purple, paler purple, purplish-blue, blue, grayish-blue and gray to lighter or darker shades of brown, grayish-brown and purplish-brown; (b) from darker to lighter greenish-brown or from bluish-green to greenish-brown; and (c) from dark brown or fl to lighter brown.
Crystals with similar pleochroic cores in the granite at Dromana were derived from the assimilation of hornblende diorite schlieren, and as these crystals were formed in the schlieren during the period of instability of the hornblende, when granitization was in progress, they would be xenocrystal when occurring in the granite.
www.minsocam.org /MSA/collectors_corner/arc/apatitevic.htm   (2356 words)

  
 Reflection Pleochroism
Pleochroism is an optical effect where the mineral appears to change colors as it is rotated while illuminated by plane polarized light.
The polarizers are not crossed to observe pleochroism.
Minerals which are pleochroic (non-isotropic minerals) are also bireflectant.
webmineral.com /help/RLPleochroism.shtml   (240 words)

  
 Dichroism
Pleochroism or dichroism is the change in color evident as the mineral is rotated under plane-polarized light.
The primary cause of dichroism or pleochroism in minerals is due to adsorption of particular wavelengths of light.
Pleochroic colors are observed and recorded in the mineral data and are generally diagnostic of the particular mineral.
webmineral.com /help/Dichroism.shtml   (222 words)

  
 Alphabetical References   (Site not responding. Last check: 2007-10-07)
Faye GH, Harris DC (1969) On the colour and pleochroism in andalusite from Brazil.
Faye GH, Hogarth DD (1969) On the origin of 'reverse pleochroism' of a phlogoite.
Faye GH, Nickel EH (1971) Pleochroism of zoisite from Tanzania.
minerals.gps.caltech.edu /REFS/F.htm   (487 words)

  
 Table 4. Monoclinic Crystal Class
weak pleochroism, weak to distinct anisotropy, weak to distinct bireflectance, moderate birefringence.
distinct pleochroism, strong anisotropy, abundant twin lamellae, distinct bireflectance.
weak pleochroism, (001), distinct pleochroism (010) and (100), quite vivid anisotropy, striking internal reflections (010) plane, weak to distinct bireflectance, moderate birefringence.
www.zonge.com /ferro/prope_13.htm   (272 words)

  
 Summit Minerals - Hidden Color: Pleochroism in Mineral Crystals
The word is not meant to mean multi-colored, such as in the swirls of lace agate or in the iridescence of labradorite.
In fact, pleochroism in all such minerals can be observed if you have a sensitive spectrophotometer.
Pleochroism in these minerals is seen when the polarizer is rotated relative to the c-axis.
home.flash.net /~summit1/collect/archive/pleo/9706.htm   (3114 words)

  
 Table 5. Orthorhombic Crystal Class
weak pleochroism, weakly to distinctly anisotropic, weak bireflectance.
distinct pleochroism in oil, strong anisotropy, distinct bireflectance in oil.
weak to distinct pleochroism, strongly anisotropic, distinct to strong bireflectance.
www.zonge.com /ferro/prope_14.htm   (220 words)

  
 IOLITE - Earrings1.com   (Site not responding. Last check: 2007-10-07)
A pleochroic stone, iolite will show many colors in a single stone including violet blue, yellow gray and a light blue.
Pleochroism is very pronounced in iolite and is seen as three different color shades in the same stone.
However, tanzanite is usually more strongly colored, its pleochroic colors vary from dark blue, green-yellow and red-purple and it has greater fire.
www.earrings1.com /47/cat47.htm?907   (167 words)

  
 Welcome to Four Seasons Gems Website!   (Site not responding. Last check: 2007-10-07)
Pleochroism is very pronounced in tanzanite and is seen as three different color shades in the same stone.
Iolite is a blue-violet gemstone variety of the mineral cordierite, has strong pleochroism and can be confused with tanzanite.
However, iolite is usually less strongly colored, its pleochroic colors vary from blue-violet to yellowish gray to blue and it has less fire.
www.fourseasonsgems.com   (356 words)

  
 Titanium in staurolite
From this and the pleochroic scheme it is further inferred that the titanium in staurolite is located in the tetrahedrally coordinated Fe site.
Staurolite is well known for its yellow color and moderate pleochroism, which follows the scheme Z yellow, Y pale yellow, and X virtually colorless.
Note that the smaller twin crystal is paler because of pleochroism and the different absorption direction, not because of sector-zoning.
www.minsocam.org /msa/collectors_corner/arc/staurolite.htm   (3441 words)

  
 Andalusite Facts and Buying Guide - JewelInfo4u
The extraordinary pleochroism occurs naturally in this gemstone but it is largely dependent on the orientation of the gemstone.
The pleochroic colours are red, green and yellow.
Cutters have to efficiently cut the stone in such a way that the phenomenon of pleochroism is highlighted and the cut shape display a blend of pleasing colours.
jewelinfo4u.com /Andalusite_Facts_and_Buying_Guide.aspx   (1293 words)

  
 Useful Mineral Differentiating Criteria
Biotite is highly colored and strongly pleochroic in shades of green or brown while muscovite is colorless in plane polarized light.
Enstitite is usually colorless, but hypersthene is frequently pleochroic in shades of pink to blue-green.
Hornblend is generally strongly colored and pleochroic in shades of yellow, green and brown.
www.ces.ncsu.edu /plymouth/programs/useful.html   (1782 words)

  
 [No title]   (Site not responding. Last check: 2007-10-07)
Biaxial negative; strong pleochroism in brown, reddish brown, and green; extinction is parallel to one excellent cleavage.
The most distinctive properties of biotite are the combination of strong pleochroism and parallel extinction.
Although hornblende has similar pleochroic colors and can be confused with biotite, hornblende has inclined extinction, not parallel extinction.
www.humboldt.edu /~jdl1/web.page.images/biotite1.html   (155 words)

  
 Iolite Facts and Buying Guide - JewelInfo4u
The phenomenon of pleochroism is exhibited strongly in this gemstone.
Stones exhibit pleochroism to the extreme extent only if it is cut appropriately.
One small wrong cut could ruin the entire effect and the stone looses its worth, as then the desired colours on the rotation of the stone are not displayed.
jewelinfo4u.com /Iolite_Facts_and_Buying_Guide.aspx   (1470 words)

  
 Pleochroism   (Site not responding. Last check: 2007-10-07)
Because of the different absorptions, the turning out color that the direction of the beam is observed second varied incident; in the case of strong differences of absorption the phenomenon is observable also to naked eye and the stone will appear of various color when swirled.
The crystals that have two various colors are called dichroic, if the various colors are three are called trichroic; the pleochroism can be of several levels: null, weak, mean and high.
In order to observe in facilitated way the pleochroism an instrument called dichroscopeis is used, that it concurs to observe in contemporary, one next to the other, the different colors of one stone (Photo1).
www.minerali.it /pleoenglish.html   (189 words)

  
 ACLAND - LoveToKnow Article on ACLAND   (Site not responding. Last check: 2007-10-07)
In its crystallo-graphic characters it is close to ordinary pyroxene (augite and diopside), being monoclinic and having nearly the same angle between the prismatic cleavages.
There are, however, important differences in the optical characters: the birefringence of acmite is negative, the pleochroism is strong and the extinction angle on the plane of symmetry measured to the vertical axis is small (3-5).
The hardness is 6-65, and the specific gravity 3'55-Crystals are elongated in the direction of the vertical axis, and are flish green (aegirite) or dark brown (acmite) in color.
www.1911ency.org /A/AC/ACLAND.htm   (893 words)

  
 [No title]   (Site not responding. Last check: 2007-10-07)
Olivine is a common constituent of basic igneous rocks where it’s composition is magnesium rich; it is usually accompanied by a clinopyroxene, which has a brownish colour, where as the olivine is almost colourless or slightly greenish in colour compared with the pyroxene.
Colour and Pleochroism in PPL: Weakly pleochroic, pink to green.
Biotite is a common rock forming mineral and is common in most forms of igneous as well as regional and contact metamorphic rocks.
www.jmorland.freeserve.co.uk /Page2.htm   (916 words)

  
 pleochroism.html   (Site not responding. Last check: 2007-10-07)
Different colors or intensities of uniaxial and biaxial minerals can also be associate with particular vibrational directions of light rays when split in two.
If a mineral changes color or the intensity of the color changes as the mineral is observed on a rotating microscope stage, then that is called pleochroic.
Pleochroism is produced because the two rays of light are absorbed in different vibrational directions as they pass through the mineral.
www.uvm.edu /~swgordon/231-03/finprojects/Lacey/pleoch.html   (109 words)

  
 Minerals under the Microscope: Earth Sciences: University of Bristol
The anistropy shown by non-cubic crystals in their physical properties can also be shown by their absorption - this phenomenon is called pleochroism and is a useful distinguishing property.
Pleochroism is apparent in thin section when minerals undergo a colour change as they are rotated in plane polarised light.
Look at the variation in colour between these two; this is pleochroism.
www.gly.bris.ac.uk /www/teach/opmin/mins.html   (2153 words)

  
 Andalusite - Information about Gemstones by Chard
The differential selective absorption of the ordinary ray and the extraordinary ray in uniaxial stones (dichroism), or of the three rays corresponding to the three principal vibration directions in biaxial stones (trichroism).
Its pleochroic colours are red, green and yellow.
Because of the pleochroism, the colour of an andalusite can be affected considerably by the direction in which it is cut.
www.24carat.co.uk /andalusite.html   (468 words)

  
 Pleochroism   (Site not responding. Last check: 2007-10-07)
To describe the pleochroism for uniaxial minerals must specify the colour which corresponds to the ordinary and extraordinary rays.
Selective absorption as a function of both wavelength and crystallographic direction gives rise to pleochroic minerals (such as biotite).
Pleochroism is an optical effect where the mineral...
www.gems21.com /directory/pleochroism.html   (443 words)

  
 Why Is Asbestos Fibrous
For example a blue mineral is one that absorbs red and yellow wavelengths of light, leaving only blue wavelengths to pass through the sample on the microscope stage and eventually reach our eyes.
In pleochroic minerals, the absorption of light is dependent upon the direction in which it travels through the crystal.
For example, in a mineral that is pleochroic from yellow to green, light traveling through the mineral in one direction has the red and blue light absorbed (leaving only yellow) whereas light traveling through the other direction has only the red light absorbed (leaving blue and yellow light that mix to form green light).
academic.brooklyn.cuny.edu /geology/powell/core_asbestos/analyze/pleochroism/pleochroism.htm   (308 words)

  
 [No title]   (Site not responding. Last check: 2007-10-07)
Biaxial -; strong pleochroism, blue to violet to colorless to pale brown; amphibole cleavage.
Occurs in low grade metamorphic rocks, associated with white mica, albite, quartz, chlorite, epidote, and occasionally lawsonite and jadeite.
On the right is a crossed polarizers view of a glaucophane schist with a large, isotropic garnet in the center, surrounded by highly birefringent glaucophane and white mica.
www.humboldt.edu /~jdl1/web.page.images/glaucophane1.html   (105 words)

  
 Minerals. Type localities of Utah
Pleochroism is X = yellow, Y = orange-yellow, Z = red.
Stringhamite is pleochroic, X = light grey blue, Y = light blue, Z = dark blue.
Pleochroic: X = light brown, Y = dark brown, Z = yellow green.
www.rocks4u.com /utahminerals.htm   (8194 words)

  
 orthopyroxene.html   (Site not responding. Last check: 2007-10-07)
The similar appearance in plane light of orthopyroxene and clinopyroxene are highlighted in this image.
Note that both grains lack any clear color, although colored and pleochroic varieties are common.
distinguished from cpx by: 1) lower birefringence, 2) parallel extinction, 3) pale color, weak pleochroism, 4) most common opx is optically negative, and 5) high 2V angle.
www.uvm.edu /~swgordon/231-03/finprojects/Lacey/orpyr.html   (215 words)

  
 Reflection Anisotrophism
Anisotrophism is an optical effect where the mineral appears to change colors as it is rotated while illuminated by crossed polarized light.
The polarizers are not crossed as in the case to observe reflection pleochroism.
Minerals which are pleochroic or bireflectant are generally also anisotropic.
webmineral.com /help/RLAnisotrophism.shtml   (278 words)

  
 Biotite
pleochroism in biotite: the same crystal rotated through 90° to show the change in body colour
Pleochroic halo around a crystal of zircon in biotite.
Top right, the same group of crystals rotated to show the intense pleochroism.
www.ucl.ac.uk /~ucfbrxs/PLM/biotite.html   (147 words)

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