Alexandrite
Alexandrite is a color changing variety of chrysoberyl. It is a phenomenal gem in several senses of the word. First, it exhibits a "phenomenon" in that it changes colors depending on the quality of the light that passes through it. Second, a fine alexandrite is phenomenally beautiful. Third, quality alexandrites are phenomenally expensive.
The single most important factor in the value of an alexandrite is its color change. Alexandrites can come in a range of colors, from yellow-green through blue-green in daylight, and from reddish orange to a deep plum purple in incandescent light. Alexandrites that change from a pure, or very slightly bluish, green to a slightly purplish red are the most valuable. More bluish or yellowish colors decrease the value somewhat, depending on how far from the "ideal" colors they are.
Alexandrites can vary in degree of color change. The finest stones readily change color with changes in lighting, with the new color completely replacing the old color throughout the gem. Such stones are said to have a 100 percent color change, and command a premium value. Many alexandrites change colors less completely, with some facets remaining green while others change to red. Often, the color change is difficult to see under bright lights of any type. These stones are considered to have a partial color change. The degree of color change is often given as a percentage.
Looking straight into the table (top facet) of the gem under a fluorescent lamp, the stone will be green. Looking into the table of the same gem under an incandescent lamp, the number of facets that turn red corresponds to the percentage of color change. Note that any alexandrite with a partial color change will change more completely under a 40 watt incandescent bulb than under a 75 watt bulb, because the light from the lower wattage lamp is redder to start.
Ideally, an alexandrite will resemble a fine emerald in daylight, when it will shine with a rich green color. The same gem, in incandescent light, will become a deep red, probably with a strong purplish tint. In firelight, the red will be even more pronounced.
The Gemological Institute of America (GIA) classifies alexandrite as a Type 2 gemstone. This means that a truly flawless natural alexandrite is not something one can reasonably expect at any price. Even the best alexandrites will have some tiny inclusions that can be seen with a loupe. Even inclusions that are visible to the unaided eye have a minimal effect on the value of alexandrite, as long as there are not too many of them.
Fine alexandrites are transparent and lively, exhibiting all the sparkle that one expects from any fine gemstone. More commonly, alexandrites will seem a bit dull because of "clouds" of tiny crystal inclusions, because the color is very dark, or both.
Because alexandrite crystals are rarely found in an ideal shape, and the material is too valuable to waste, a truly well cut alexandrite is a rarity. Most alexandrite gems are cut to maximize the carat weight from the rough stone, with all other considerations a distant second. Because of this, most gems are cut as ovals with a shallow pavilion, resulting in a "window," or a region where the gem loses luster. Even though this practice produces larger but less beautiful jewels, the quality of the cut does not seem to be a major factor in setting the value of an alexandrite.
The single most important factor in the value of an alexandrite is its color change. Alexandrites can come in a range of colors, from yellow-green through blue-green in daylight, and from reddish orange to a deep plum purple in incandescent light. Alexandrites that change from a pure, or very slightly bluish, green to a slightly purplish red are the most valuable. More bluish or yellowish colors decrease the value somewhat, depending on how far from the "ideal" colors they are.
Alexandrites can vary in degree of color change. The finest stones readily change color with changes in lighting, with the new color completely replacing the old color throughout the gem. Such stones are said to have a 100 percent color change, and command a premium value. Many alexandrites change colors less completely, with some facets remaining green while others change to red. Often, the color change is difficult to see under bright lights of any type. These stones are considered to have a partial color change. The degree of color change is often given as a percentage.
Looking straight into the table (top facet) of the gem under a fluorescent lamp, the stone will be green. Looking into the table of the same gem under an incandescent lamp, the number of facets that turn red corresponds to the percentage of color change. Note that any alexandrite with a partial color change will change more completely under a 40 watt incandescent bulb than under a 75 watt bulb, because the light from the lower wattage lamp is redder to start.
Ideally, an alexandrite will resemble a fine emerald in daylight, when it will shine with a rich green color. The same gem, in incandescent light, will become a deep red, probably with a strong purplish tint. In firelight, the red will be even more pronounced.
The Gemological Institute of America (GIA) classifies alexandrite as a Type 2 gemstone. This means that a truly flawless natural alexandrite is not something one can reasonably expect at any price. Even the best alexandrites will have some tiny inclusions that can be seen with a loupe. Even inclusions that are visible to the unaided eye have a minimal effect on the value of alexandrite, as long as there are not too many of them.
Fine alexandrites are transparent and lively, exhibiting all the sparkle that one expects from any fine gemstone. More commonly, alexandrites will seem a bit dull because of "clouds" of tiny crystal inclusions, because the color is very dark, or both.
Because alexandrite crystals are rarely found in an ideal shape, and the material is too valuable to waste, a truly well cut alexandrite is a rarity. Most alexandrite gems are cut to maximize the carat weight from the rough stone, with all other considerations a distant second. Because of this, most gems are cut as ovals with a shallow pavilion, resulting in a "window," or a region where the gem loses luster. Even though this practice produces larger but less beautiful jewels, the quality of the cut does not seem to be a major factor in setting the value of an alexandrite.
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