GIA Colored Stones Exam 451-500 Flashcards
Interaction of two light rays traveling the same path.
interference
A rainbow effect created when light is broken up into spectral hues by thin layers.
iridescence
A broad flash of color in labradorite feldspar that disappears when the gem is moved.
labradorescence
A two_toned effect seen when a chatoyant gem is positioned at right angles to a light source.
milk and honey
Direction of single refraction in a doubly refractive gem.
optic axis
Iridescence seen in some natural and cultured pearls and mother_of_pearl.
orient
An unusual optical effect displayed by a gem.
phenomenon
The flashing rainbow colors in opal.
play_of_color
When a gem shows different body_colors from different cystal directions.
pleochroism
Change in speed and possible change in direction of light as it travels from one material to another.
refraction
Process by which a material absorbs some components of visable light and transmits others.
selective absorption
When a gem’s crystal structure doesn’t change incoming light other than by refraction and absorption.
single refractive
Elements that can selectively abrorb some wavelengths of visible light and produce color in gems.
Transition elements
Which gemstone occurs in almost every color?
Tourmaline
The first impression of an object’s basic color is its ___________ .
hue
Generally; cool_colored hues with low saturation look ____________ .
grayish
Use trade terms that imply geographic origin only if the ________________ .
gem’s actual source is known
Which trade term describes certain tourmalines? A. Paraiba B. Kashmir C. Sandawana D. Mozambique
A. Paraiba
What is the GIA Colored Stone Grading System’s abbreviation for a “slightly purplish red hue” ?
slpR
In practice; what GIA Colored Stone Grading levels apply to grading transparent colored stones?
2 through 8
A see_through area cut in a transparent gemstone’s bodycolor that usually results from the way the gem was cut is called _____________ .
a window
A window usually differs from the rest of the stone in _______________ .
saturation
Extinction results from ____________ .
deep pavilions
The color of the background for grading a colored stone should be ______ .
neutral.
What type of lighting is best for grading color in a colored stone?
daylight_equivalent fluorescent
Higher levels of saturation are usually found in stones with ___________ .
medium to medium_dark tones.
What two coloring agents are usually responsible for color change in gemstones?
chromium and iron
Emission of visable light by a material when it’s exposed to invisable ultraviolet radiation is called __________ .
fluorescence
You should judge a gemstone’s beauty and value only by comparing it to what?
A sample of its own species or variety.
Cutting compromises that save weight can also cause what __________; __________ or ___________ .
windows; extinction; both
What do you use; in a buying situation; when you cannot control the lighting conditions?
comparison stones or color samples
A laboratory_created gem with essentially the same chemical composition; crystal structure; and properties as its natural counterpart is called a _____________ .
synthetic
The two main types of processes for synthetic gem production are melt and ____________ .
solution
Low cost and high volume characterize which synthetic process?
flame fusion
What synthetic process developed rapidly due to laser research in the late 1960’s?
pulling
What process uses a heating unit to pass over a rotating solid rod of chemicals until it forms a synthetic crystal?
floating zone
What process dissolves nutrients in chemicals to form synthetic crystals?
flux growth
The crucibles that work best for flux growth are made of what material?
platinum
The hydrothermal growth process is the only method used to produce which synthetic gem?
quartz
What synthetic process uses an autoclave?
hydrothermal growth
Synthetic opal is grown using microscopic silica spheres that are produced by _________ .
precipitation
What process involves heating finely ground powder; sometimes under pressure; to produce a fine_grained solid material?
ceramic
Synthetic turquoise is most likely produced by what process?
ceramic
The flux used in the flux process is a solid material that; when molten it ____________ .
disolves other materials
The hydrothermal synthetic process requires what?
a pressurized steel container and crushed chemical ingredients
A snakeskin structural pattern is typical of what synthetic?
synthetic opal
A process in which powdered chemicals are dropped through a high_temperature flame onto a rotating pedestal to produce a synthetic crystal.
flame fusion
A melt process where a heating unit passes over a rotating solid rod of chemicals until it forms a synthetic crystal.
floating zone
A process in which nutrients dissolve in heated chemicals; then cool to form synthetic crystals.
flux growth
A process in which nutrients disolve in a water solution at high temperature and pressure; then cool to form synthetic crystals.
hydrothermal growth
