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GIA Graduate Gemologist - GEM 220 - Colored Stones > Assignment 4 - Gems & Light > Flashcards

Assignment 4 - Gems & Light Flashcards

1
Q

The distance between two adjacent high points of an energy wave.

A

Wavelength

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2
Q

Process by which a material absorbs some
components of visible light and transmits others.

A

Selective absorption

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3
Q

A pattern of dark vertical lines or bands shown by
certain gems when viewed through a spectroscope.

A

Absorption spectrum

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4
Q

Elements that can selectively absorb some
wavelengths of visible light and produce color in gems.

A

Transition elements

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5
Q

A gem colored by trace elements in its crystal structure.

A

Allochromatic

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6
Q

A gem colored by an element that is an essential part of its chemical composition.

A

Idiochromatic

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7
Q

The movement of electrons back and forth between ions, causing the selective
absorption of light.

A

Charge transfer

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8
Q

A process where two transition elements with different valences exchange electrons to selectively absorb light.

A

Intervalence charge transfer

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9
Q

A small defect in the crystal structure of a material that can absorb light and give rise to a color.

A

Color center

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10
Q

Exposing a gem to manmade radiation to change or improve its color.

A

Irradiation

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11
Q

Emission of visible light by a material when it’s
stimulated by ultraviolet or X-ray radiation.

A

Fluorescence

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12
Q

Continued emission of visible light after UV or X-
ray stimulation stops.

A

Phosphorescence

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13
Q

Change in speed and possible change in direction of light as it travels from one material to another.

A

Refraction

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14
Q

The appearance of double
images of a gemstone’s facet junctions
on the side opposite the viewer.

A

Doubling

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15
Q

When a gem’s crystal structure splits light into two rays that each travel at a slightly different speed and direction.

A

Double refraction

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16
Q

When a gem’s crystal structure doesn’t change incoming light other than by refraction and absorption.

A

Single refraction

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17
Q

Direction of single refraction in a doubly refractive gem.

A

Optic axis

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18
Q

When a gem shows different bodycolors from different crystal directions.

A

Pleochroism

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19
Q

The separation of white light into spectral colors.

A

Dispersion

20
Q

Interaction between two light rays with the same wavelengths as they travel along the same path.

A

Interference

21
Q

A rainbow effect created when light is broken up into spectral hues by thin layers.

A

Iridescence (Orient)

22
Q

Iridescence seen in some natural and cultured pearls and mother-of-pearl.

A

Orient

23
Q

A special kind of interference phenomenon that
produces patches of pure spectral colors.

A

Diffraction

24
Q

The flashing rainbow colors in opal, produced by the interaction of visible light with the gem’s microscopic internal structure of stacked silica spheres.

A

Play-of-color

25
Q

A broad flash of color in labradorite feldspar that
disappears when the gem is moved.

A

Labradorescence

26
Q

The cloudy bluish white light in a moonstone, caused by scattering of light.

A

Adularescence

27
Q

Bands of light in certain gems, caused by reflection of light from many parallel, needle-like
inclusions or hollow tubes.

A

Chatoyancy

28
Q

A two-toned effect seen when a chatoyant gem is
positioned at right angles to a light source.

A

Milk and honey

29
Q

Crossing of chatoyant bands, creating a star in the dome of a cabochon.

A

Asterism

30
Q

A glittery effect caused by light reflecting from small, flat inclusions within a gemstone.

A

Aventurescence

31
Q

A distinct change in gem color under different types of lighting.

A

Color change

32
Q

Why are some gem colors more rare and more valuable than others?

A

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.

33
Q

Which element produces the brightest reds and greens?

A

Chromium causes the most desirable
red and green gem colors.

34
Q

How can the same impurity element cause different colors in different gems?

A

Crystal structure variations result in the
same transition element causing
different colors in different gems.

35
Q

How does a gem’s interaction with light cause its color?

A

Interaction of electrons with visible light
causes most selective absorption
related gem colors.

36
Q

How does crystal structure influence the way a gem interacts with light?

A

Gems handle light in different ways because their internal symmetry and crystal structure are different. Their structural differences produce readily visible and measurable effects.

37
Q

What causes double refraction?

A

Some gems do more than just slow light down and change its direction: they split light into two separate rays.

38
Q

What causes pleochroism?

A

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.

39
Q

What causes opal’s spectacular colors?

A

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.

40
Q

What causes star and cat’s-eye effects in some gems?

A

Inclusions.

41
Q

What causes the change-of-color effect in alexandrite and some other gems?

A

Because the gem’s absorption is closely balanced between red and green, its color varies with the type of lighting it’s viewed under.

42
Q

Which element causes the color of both almandine and peridot?

A. Iron

B. Cobalt

C. Titanium

D. Chromium

A

A.
Iron

43
Q

Which element causes variety of gem
colors than any other transition element.

A

Iron causes a greater variety of gem
colors than any other transition element.

44
Q

Which gem can show three pleochroic colors?

A. Iolite

B. Ruby

C. Sapphire

D. Tourmaline

A

A. Iolite

45
Q

Which element does chromium substitute for to cause ruby’s red?

A. Silicon

B. Titanium

C. Beryllium

D. Aluminum

A

D. Aluminum

46
Q

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.

A

B. iron and titanium.

GIA Graduate Gemologist - GEM 220 - Colored Stones (27 decks)

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