Assignment 4 - Gems & Light Flashcards
The distance between two adjacent high points of an energy wave.
Wavelength
Process by which a material absorbs some
components of visible light and transmits others.
Selective absorption
A pattern of dark vertical lines or bands shown by
certain gems when viewed through a spectroscope.
Absorption spectrum
Elements that can selectively absorb some
wavelengths of visible light and produce color in gems.
Transition elements
A gem colored by trace elements in its crystal structure.
Allochromatic
A gem colored by an element that is an essential part of its chemical composition.
Idiochromatic
The movement of electrons back and forth between ions, causing the selective
absorption of light.
Charge transfer
A process where two transition elements with different valences exchange electrons to selectively absorb light.
Intervalence charge transfer
A small defect in the crystal structure of a material that can absorb light and give rise to a color.
Color center
Exposing a gem to manmade radiation to change or improve its color.
Irradiation
Emission of visible light by a material when it’s
stimulated by ultraviolet or X-ray radiation.
Fluorescence
Continued emission of visible light after UV or X-
ray stimulation stops.
Phosphorescence
Change in speed and possible change in direction of light as it travels from one material to another.
Refraction
The appearance of double
images of a gemstone’s facet junctions
on the side opposite the viewer.
Doubling
When a gem’s crystal structure splits light into two rays that each travel at a slightly different speed and direction.
Double refraction
When a gem’s crystal structure doesn’t change incoming light other than by refraction and absorption.
Single refraction
Direction of single refraction in a doubly refractive gem.
Optic axis
When a gem shows different bodycolors from different crystal directions.
Pleochroism
The separation of white light into spectral colors.
Dispersion
Interaction between two light rays with the same wavelengths as they travel along the same path.
Interference
A rainbow effect created when light is broken up into spectral hues by thin layers.
Iridescence (Orient)
Iridescence seen in some natural and cultured pearls and mother-of-pearl.
Orient
A special kind of interference phenomenon that
produces patches of pure spectral colors.
Diffraction
The flashing rainbow colors in opal, produced by the interaction of visible light with the gem’s microscopic internal structure of stacked silica spheres.
Play-of-color
A broad flash of color in labradorite feldspar that
disappears when the gem is moved.
Labradorescence
The cloudy bluish white light in a moonstone, caused by scattering of light.
Adularescence
Bands of light in certain gems, caused by reflection of light from many parallel, needle-like
inclusions or hollow tubes.
Chatoyancy
A two-toned effect seen when a chatoyant gem is
positioned at right angles to a light source.
Milk and honey
Crossing of chatoyant bands, creating a star in the dome of a cabochon.
Asterism
A glittery effect caused by light reflecting from small, flat inclusions within a gemstone.
Aventurescence
A distinct change in gem color under different types of lighting.
Color change
Why are some gem colors more rare and more valuable than others?
Color variations from gem to gem make real differences in value. The gems with the best colors are always more attractive, more
rare, and more highly valued than the others. The causes of color are what make those color and value differences possible.
Which element produces the brightest reds and greens?
Chromium causes the most desirable
red and green gem colors.
How can the same impurity element cause different colors in different gems?
Crystal structure variations result in the
same transition element causing
different colors in different gems.
How does a gem’s interaction with light cause its color?
Interaction of electrons with visible light
causes most selective absorption
related gem colors.
How does crystal structure influence the way a gem interacts with light?
Gems handle light in different ways because their internal symmetry and crystal structure are different. Their structural differences produce readily visible and measurable effects.
What causes double refraction?
Some gems do more than just slow light down and change its direction: they split light into two separate rays.
What causes pleochroism?
Light traveling down the length of the crystal
encounters a different structure than light traveling across it. As a result, the light is absorbed differently. This results in a pleochroic gem—one that shows different colors when viewed along different crystal directions.
What causes opal’s spectacular colors?
Diffraction is a special type of interference phenomenon. Unlike iridescence, it produces pure spectral colors rather than combinations of several spectral colors. Rather than producing areas of lightness and darkness, it produces the pure spectral hues red, orange, yellow, green, blue, and violet.
What causes star and cat’s-eye effects in some gems?
Inclusions.
What causes the change-of-color effect in alexandrite and some other gems?
Because the gem’s absorption is closely balanced between red and green, its color varies with the type of lighting it’s viewed under.
Which element causes the color of both almandine and peridot?
A. Iron
B. Cobalt
C. Titanium
D. Chromium
A.
Iron
Which element causes variety of gem
colors than any other transition element.
Iron causes a greater variety of gem
colors than any other transition element.
Which gem can show three pleochroic colors?
A. Iolite
B. Ruby
C. Sapphire
D. Tourmaline
A. Iolite
Which element does chromium substitute for to cause ruby’s red?
A. Silicon
B. Titanium
C. Beryllium
D. Aluminum
D. Aluminum
In many blue sapphires, the intervalence charge transfer that causes the color is between
A. iron and iron.
B. iron and titanium.
C. chromium and iron.
D.oxygen and oxygen.
B. iron and titanium.
