GIA Colored Stones Exam 351-400 Flashcards
What easily distinguishes colorless zircon from diamond or synthetic cubic zirconia?
strong double refraction
Why does zircon need care in handling and wear?
brittleness
What is the trade term for a vibrant green tourmaline that is colored by traces of vanadium; chromium or both?
chrome tourmaline
What is the trade term for blue tourmaline?
indicolite
Gems that show color zoning with two or more colors is known as ___________ .
parti_colored
What is the trade name for a pink to red elbaite tourmaline?
rubellite
What is the refractive nature of garnet?
single
How do gemologists classify garnets?
by their chemistry and their properties.
What do dealers base their garnets on?
color or origin
What type of garnet has properties that make it an effective and less expensive alternative to emerald?
tsavorite
What is the best color for tsavorite?
vivid green; medium to medium_dark tone
Tsavorite is colored by what trace element?
vanadium
In what area is tsavorite mostly mined?
East Africa
Name a transparent green variety of andradite?
demantoid garnet
Demantoid garnet is colored by what trace elements?
a mixture of chromium and iron
What is the most valuable orange garnet?
spessartite
Name a transparent orange to cinnamon_colored variety of the grossularite species of garnet?
hessonite
Rhodolite and most red garnets are a mixture of what two garnet species?
pyrope and almandite
Dark purplish red to light reddish purple.
Rhodolite’s color range.
What is the most valuable red garnet?
rhodolite
What area has been the most important source of rhodolite since the 1960’s?
East africa
What type of garnet is used in inexpensive mass_market jewelry?
dark_toned; reddish brown calibrated pyrope_almandite
Color_change garnets are comprised of a mixture of what species?
pyrope_spessartite
What trace element is the coloring agent in color_change garnet?
vanadium
In spinel; what trace element causes the strength of red in garnet?
The higher the chromium content the stronger the red
What is the most rare and valuable spinel hue?
red
What gemstone forms in the same metamorphic rock as corundum and is found in the same alluvial deposits?
spinel
Why have many people not seen a natural spinel?
Because natural spinel is rare and synthetic spinel is common
A cabochon with a curved; undercut bottom; designed to lighten the tone of the gem material is called a ___________ .
hollowback
The substitution of one chemical element for another in the crystal structure of a mineral is called _________ .
isomorphous replacement
Where is spessartite most commonly found?
pegmatite veins
Which of the following has the widest color range? A. Rhodolite B. Almandite C. Spessartite D. Grossularite
D. Grossularite
Tsavorite and hessonite are both varieties of __________ .
grossularite
All garnets have essentially the same __________ .
crystal structure
Rhodolite is a mixture of what varieties of garnet?
almandite and pyrope
Mandarin garnet has been used as a trade name for __________ .
spessartite
Dematoid was first discovered in what country?
Russia
Tsavorite is colored by what element?
vanadium
The intense red color of spinel is caused by what element?
chromium
Horsetail inclusions are found in what type of garnet?
dematoid
The most important source of rhodolite in recent years has been in what area?
East Africa
The most valuable spinel color is _________ .
red
The most desirable; vibrant; and rare blue natural spinels are colored by what elements?
cobalt and iron
Light that eventually returns to the eye after entering a gem through the crown; reflecting off its pavilion facets; and exiting back through the crown is known as __________ .
brilliance
A cutting style with triangular or kite_shaped facets that radiate from the center toward the girdle is called a __________ .
brilliant cut
A smoothly rounded polished gem with a domed top and a flat or curved base is called a _________ .
cabochon
A gem carving style in which the design; often a women’s profile; projects slightly from a flat or curved surface is called a ________ .
cameo
Removing heavily included sections from gemstone rough by carefully tapping it with a small hammer is called ___________ .
cobbing
The top part of the gem above the girdle is called __________ .
the crown
The relationship of the height of a gem’s crown to the depth of tis pavilion; judged by viewing its profile is called _____________ .
Crown/height to pavillion/depth ratio
