GIA Colored Stones Exam 151-200

Question 1

What are the most widespread minerals on earth?

Answer 1

Feldspars

Question 2

How many cleavage directions are found in feldspar; spodumene and diopside?

Answer 2

Two

Question 3

What three basic chemical elements do all feldspars contain?

Answer 3

aluminum; oxygen; silicon

Question 4

Moonstone is a variety of ________ .

Answer 4

Orthoclase

Question 5

In which era did moonstone go out of style?

Answer 5

Art Deco

Question 6

What color is the finest adularescence of the finest moonstone?

Answer 6

Blue

Question 7

Tiny tension cracks in moonstone are called what?

Answer 7

Centipedes

Question 8

Rainbow moonstone is a trade term for a type of ________ .

Answer 8

Labradorite

Question 9

Spectrolite is a variety of _________ .

Answer 9

Labrodorite

Question 10

The greenish blue feldspar that has gridlike white streaks and resembles turquoise is called __________ .

Answer 10

Amazonite

Question 11

Medium green.

Answer 11

Hiddenite

Question 12

The scattering of light by stacked; alternating mineral layers?

Answer 12

Moonstone’s adularescence

Question 13

What selling point is used for sunstone from Oregon?

Answer 13

It isn’t treated

Question 14

The high clarity and lack of treatment make what stone an attractive emerald alternative?

Answer 14

Chrome diopside.

Question 15

What causes sunstone’s redish or golden sheen?

Answer 15

small inclusions

Question 16

What causes sunstone’s glittering reflections?

Answer 16

larger inclusions

Question 17

Intense pink and intense violetish purple.

Answer 17

Kunzite

Question 18

Opal is composed of primarily of __________ .

Answer 18

Silica

Question 19

When did most opal form?

Answer 19

15 to 30 million years ago.

Question 20

What is the percentage of water that most opal contains?

Answer 20

3 to 10 percent

Question 21

What is semi_black opal’s background color?

Answer 21

grayish

Question 22

What is the transparency of gray_based black opal?

Answer 22

opaque

Question 23

What is the transparency range of white opal?

Answer 23

translucent to opaque

Question 24

The type of matrix found as a layer in finished boulder opal is comprised of __________ .

Answer 24

ironstone

Question 25

Experts think fire opal's background color is caused by _________ .

Answer 25

Iron impurities

Question 26

In opal; a pattern of large distinct; usually rectangular patches of play_of_color with edges that touch each other is called __________ .

Answer 26

Harlequin

Question 27

Play_of_color that's seen only when light travels through an opal to the eye is called _________ .

Answer 27

Contra luz

Question 28

Where were the first black opals discovered?

Answer 28

New South Wales; Australia

Question 29

What is the first step in evaluating an opal?

Answer 29

Determine its type

Question 30

Which treatment involves immersing opal in concentrated sulfuric acid?

Answer 30

sugar

Question 31

Who created the first marketable synthetic opal>

Answer 31

Pierre Gilson

Question 32

Plastic imitation opal was first marketed in the late 1980's in what country?

Answer 32

Japan

Question 33

What is precious opal made of?

Answer 33

Billions of uniform; submicroscopic silica spheres; stacked in an orderly pattern.

Question 34

What type of opal commands the highest prices?

Answer 34

black

Question 35

What type of opal makes up the bulk of commercial_quality on the market?

Answer 35

white

Question 36

What makes boulder opal the most durable?

Answer 36

the matrix backing

Question 37

Uniform red_orange to bright red color

Answer 37

Finest fire opal

Question 38

What is one of the few opal types that is cut into a faceted gem?

Answer 38

fire opal

Question 39

What three things combine to create and opal's unique beauty?

Answer 39

Color; Pattern; Clarity

Question 40

How are opals divided into types?

Answer 40

by background color

Question 41

What is the rarest play_of_color?

Answer 41

Displays hues across the entire spectrum.

Question 42

What is considered the most valuable play_of_color hue?

Answer 42

red

Question 43

In general what is the most preferred play_of_color pattern?

Answer 43

large; closely arranged color patches.

Question 44

What percentage of the world's total opal supply comes from Australia?

Answer 44

90%

Question 45

What country is the major source for fire opal?

Answer 45

Mexico

Question 46

Commercial_quality white opal dominates what country's market?

Answer 46

the US

Question 47

What three things should be kept consistant when evaluating opal?

Answer 47

conditions; methods; samples

Question 48

In opal; very small patches or "dots" of play_of_color is known as _________ .

Answer 48

Pinfire

Question 49

Large areas of play_of_color is called _______ .

Answer 49

Flash

Question 50

An opal with a gray background that appears opaque is known as a __________ .

Answer 50

Semi_black opal