Gem colours Flashcards
What causes colour zoning
If conditions change during growth—for example, if a gem crystal receives greater or lesser amounts of color-causing nutrients—it will display bands of slightly different colors.
What are gems with two or more distinct color zones called
parti-coloured gems
What causes gems to display colour
depending on how they absorb and return light, their structure, and which combination of chemicals they contain.
What determines the quality of a bi-coloured gem
determined by how attractive and complementary the combination is, as well as by the location of the separation
What is pleochroism
From the Greek for “having many colors.” Pleochroic gems show different bodycolors from different viewing directions.
What colour is tanzanite
Tanzanite is a popular gem with pleochroism that can be appreciated with the unaided eye. It looks violet-blue from some directions and purple from others. Gem cutters sometimes cut tanzanite rough to feature mostly purple in the finished gems and other times mostly blue.
The choice depends on the quality of the tanzanite rough and the direction of crystal growth. Cutters fashion fine-quality tanzanite to emphasize the blue color because that commands a higher price. But even the most valuable faceted tanzanites don’t look totally blue. The attractive purple companion color always shines through.
What is a window in a stone
When you look down at a gem from above and see a gap in its bodycolor—an area of weaker color—that’s a window. Windows are usually caused by light leaking from the bottom of the stone. By creating a see-through effect, a window can make a gem’s bodycolor uneven and ruin its appearance. If a gem’s bodycolor is very dark, however, a window can lighten it a little and make the stone more appealing.
What is extinction in a stone
The result of the way a colored stone is cut. Extinction is the appearance of dark areas in a faceted gem. These dark areas shift position as you move the stone. While it can be seen in any stone, it’s seen most often in gems with darker bodycolors, such as ruby, red garnet, and blue sapphire.
What is body colour
A gems main colour
what is a phenomenal gem
but what about gemstones that glint or glow with subtle hues or special effects that defy simple description? These are the phenomenal gemstones, and their striking optical effects set them apart as unique. Examples are moonstone, opal, fire agate.. heir dazzling special effects from the way their structures interact with light. Their phenomenal colors and effects might appear to float inside or outside the gem’s basic bodycolor.
What is dispersion
As you’ve learned, white light is actually made up of all the colors of the rainbow. When you see a rainbow in the sky after a rainstorm, or when a glass prism projects a spectrum on the wall, you’re seeing the bending and splitting of white light into its component colors. This is called dispersion.
What is adularescence
When light strikes moonstone’s alternating growth layers, the result is a soft, delicate, haunting gleam of color
Which gems can change colour
Alexandrite, a chrysoberyl. Other stones, like corundum, spinel, and garnet, can show color change, but it occurs most often in Alexandrite.
What colour is Alexandrite
An alexandrite’s value depends on the hue, tone, and saturation of the two colors it shows and the degree of its color change. The finest alexandrites switch from green to purplish red. At best, however, both hues are medium in saturation. Fine alexandrite’s red looks slightly brownish and its green slightly grayish. Its color-change hues rarely if ever reach the more vivid reds and greens of fine rubies and emeralds.
What is chatoyancy
It is the cat’s-eye effect.Cat’s-eye stones contain needle-like internal characteristics, called inclusions, that lie parallel to one another like the threads on the spool.
