GIA Colored Stones Exam 151-200 Flashcards
What are the most widespread minerals on earth?
Feldspars
How many cleavage directions are found in feldspar; spodumene and diopside?
Two
What three basic chemical elements do all feldspars contain?
aluminum; oxygen; silicon
Moonstone is a variety of ________ .
Orthoclase
In which era did moonstone go out of style?
Art Deco
What color is the finest adularescence of the finest moonstone?
Blue
Tiny tension cracks in moonstone are called what?
Centipedes
Rainbow moonstone is a trade term for a type of ________ .
Labradorite
Spectrolite is a variety of _________ .
Labrodorite
The greenish blue feldspar that has gridlike white streaks and resembles turquoise is called __________ .
Amazonite
Medium green.
Hiddenite
The scattering of light by stacked; alternating mineral layers?
Moonstone’s adularescence
What selling point is used for sunstone from Oregon?
It isn’t treated
The high clarity and lack of treatment make what stone an attractive emerald alternative?
Chrome diopside.
What causes sunstone’s redish or golden sheen?
small inclusions
What causes sunstone’s glittering reflections?
larger inclusions
Intense pink and intense violetish purple.
Kunzite
Opal is composed of primarily of __________ .
Silica
When did most opal form?
15 to 30 million years ago.
What is the percentage of water that most opal contains?
3 to 10 percent
What is semi_black opal’s background color?
grayish
What is the transparency of gray_based black opal?
opaque
What is the transparency range of white opal?
translucent to opaque
The type of matrix found as a layer in finished boulder opal is comprised of __________ .
ironstone
Experts think fire opal’s background color is caused by _________ .
Iron impurities
In opal; a pattern of large distinct; usually rectangular patches of play_of_color with edges that touch each other is called __________ .
Harlequin
Play_of_color that’s seen only when light travels through an opal to the eye is called _________ .
Contra luz
Where were the first black opals discovered?
New South Wales; Australia
What is the first step in evaluating an opal?
Determine its type
Which treatment involves immersing opal in concentrated sulfuric acid?
sugar
Who created the first marketable synthetic opal>
Pierre Gilson
Plastic imitation opal was first marketed in the late 1980’s in what country?
Japan
What is precious opal made of?
Billions of uniform; submicroscopic silica spheres; stacked in an orderly pattern.
What type of opal commands the highest prices?
black
What type of opal makes up the bulk of commercial_quality on the market?
white
What makes boulder opal the most durable?
the matrix backing
Uniform red_orange to bright red color
Finest fire opal
What is one of the few opal types that is cut into a faceted gem?
fire opal
What three things combine to create and opal’s unique beauty?
Color; Pattern; Clarity
How are opals divided into types?
by background color
What is the rarest play_of_color?
Displays hues across the entire spectrum.
What is considered the most valuable play_of_color hue?
red
In general what is the most preferred play_of_color pattern?
large; closely arranged color patches.
What percentage of the world’s total opal supply comes from Australia?
90%
What country is the major source for fire opal?
Mexico
Commercial_quality white opal dominates what country’s market?
the US
What three things should be kept consistant when evaluating opal?
conditions; methods; samples
In opal; very small patches or “dots” of play_of_color is known as _________ .
Pinfire
Large areas of play_of_color is called _______ .
Flash
An opal with a gray background that appears opaque is known as a __________ .
Semi_black opal
