Assignment 4 - Gems & Light

Question 1

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

Answer 1

Wavelength

Question 2

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

Answer 2

Selective absorption

Question 3

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

Answer 3

Absorption spectrum

Question 4

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

Answer 4

Transition elements

Question 5

A gem colored by trace elements in its crystal structure.

Answer 5

Allochromatic

Question 6

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

Answer 6

Idiochromatic

Question 7

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

Answer 7

Charge transfer

Question 8

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

Answer 8

Intervalence charge transfer

Question 9

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

Answer 9

Color center

Question 10

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

Answer 10

Irradiation

Question 11

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

Answer 11

Fluorescence

Question 12

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

Answer 12

Phosphorescence

Question 13

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

Answer 13

Refraction

Question 14

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

Answer 14

Doubling

Question 15

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

Answer 15

Double refraction

Question 16

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

Answer 16

Single refraction

Question 17

Direction of single refraction in a doubly refractive gem.

Answer 17

Optic axis

Question 18

When a gem shows different bodycolors from different crystal directions.

Answer 18

Pleochroism

Question 19

The separation of white light into spectral colors.

Answer 19

Dispersion

Question 20

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

Answer 20

Interference

Question 21

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

Answer 21

Iridescence (Orient)

Question 22

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

Answer 22

Orient

Question 23

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

Answer 23

Diffraction

Question 24

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

Answer 24

Play-of-color

Question 25

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

Answer 25

Labradorescence

Question 26

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

Answer 26

Adularescence

Question 27

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

Answer 27

Chatoyancy

Question 28

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

Answer 28

Milk and honey

Question 29

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

Answer 29

Asterism

Question 30

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

Answer 30

Aventurescence

Question 31

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

Answer 31

Color change

Question 32

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

Answer 32

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.

Question 33

Which element produces the brightest reds and greens?

Answer 33

Chromium causes the most desirable red and green gem colors.

Question 34

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

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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

Question 37

What causes double refraction?

Answer 37

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

Question 38

What causes pleochroism?

Answer 38

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.

Question 39

What causes opal’s spectacular colors?

Answer 39

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.

Question 40

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

Answer 40

Inclusions.

Question 41

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

Answer 41

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

Question 42

Which element causes the color of both almandine and peridot? A. Iron B. Cobalt C. Titanium D. Chromium

Answer 42

A. Iron

Question 43

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

Answer 43

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

Question 44

Which gem can show three pleochroic colors? A. Iolite B. Ruby C. Sapphire D. Tourmaline

Answer 44

A. Iolite

Question 45

Which element does chromium substitute for to cause ruby’s red? A. Silicon B. Titanium C. Beryllium D. Aluminum

Answer 45

D. Aluminum

Question 46

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.

Answer 46

B. iron and titanium.