Pleochroic Gems and Minerals
What Are Color Changes and Color Shifts?
A “color change” stone changes color between two really obvious different colors, like Alexandrite going from bluish-green to pinkish-purple. Other more well known color change stones are Sapphire, Diaspore, and Garnet. A “color shift” stone will show a change of hues within the same basic color family, such as from yellowish green to grass green, or from yellowish red to brownish red. The latter is not really a color change, just a “shift” in color.
What Are Bi-Colored, Tri-Colored, and Parti-Colored Stones?
Bi-Colored: A mineral specimen or gemstone with two distinct colors which are clearly separated from each other. This is most commonly seen in Tourmaline and Ametrine.
Tri-Colored: A mineral specimen or gemstone with three distinct colors which are clearly separated from each other. This is most commonly seen in Tourmaline.
Parti-Colored: A mineral specimen or gemstone with multiple distinct colors blended together which are seen at different angles of observation. This is most commonly seen in Tourmaline and Sapphire. However, there are also color change and color shift Sapphires.
What Are Dichroism, Trichroism, and Pleochroism?
Dichroism: The ability of some gems to display a second color when viewed from a different angle.
Trichroism: Gems that display three different colors when viewed from different angles.
Pleochroism: The phenomenon whereby the color intensity or the actual color is different depending on the orientation in which a crystalline substance is observed. The changes in color may be seen from changes in position/angle or lighting conditions. They are true “color change” stones. The following gems and minerals, and/or some of their varieties are known to be pleochroic.
Which Gems and Minerals Are Pleochroic?
**The minerals listed below, or some of their varieties, have been reported to be pleochroic. Don’t forget, just as with fluorescent minerals, there will always be exceptions. Some minerals which you will expect to change color will not, while some you do not expect to change color may. It may only be a slight change in color, or a 100% complete change of color.
Actinolite, Alexandrite, Amblygonite, Amethyst, Anatase, Andalusite, Andesine, Anhydrite, Apatite, Aquamarine, Axinite, Azurite, Barite, Benitoite, Beryls, Brazilianite, Carletonite, Cassiterite, Charoite, Chondrodite, Chrysoberyl, Citrine, Clinohumite, Clinozoisite, Danburite, Diamond, Diaspore, Diopside, Dioptase, Dumortierite, Elbaite, Emerald, Enstatite, Euclase, Epidote, Garnet, Hiddenite, Hodgkinsonite, Hyalite Opal, Hypersthene, Idocrase, Iolite, Jeremejevite, Kornerupine, Kunzite, Kyanite, Labradorite, Lazulite, Neptunite, Orthoclase, Painite, Parisite, Peridot, Phenakite, Prasiolite, Proustite, Purpurite, Rhodonite, Rose Quartz, Ruby, Rutile, Sanidine, Sapphire, Scapolite, Scheelite, Serendibite, Sillimanite, Sinhalite, Smoky Quartz, Sphene, Spinel, Staurolite, Tantalite, Tanzanite, Topaz, Tourmaline, Tremolite, Tryphilite, Tugtupite, Vivianite, Willemite, Zircon, and Zoisite.
**And many more!
**Source: “Gemstones of the World” by Walter Schumann
*The gemstone shown at the top of the page is Alexandrite from Brazil, shown in both daylight (L) and incandescent light (R).
**If the images and/or text on any of the web pages do not appear evenly spaced and centered on your screen, which commonly occurs with AOL pages, maximize the individual page's window. That should resolve the problem.
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