GIA Colored Stones Exam 301-350 Flashcards
What characteristic determines iolites value?
predominantly blue face_up color
How can iolite be an affordable alternative to tanzanite?
It can sell for about one tenth of the price
What is the finest color_change gemstone?
Alexandrite chrysoberyl
What color_change gemstone sets the standard against which all other color_change gems are judged?
alexandrite
What trace element causes alexandrite’s color_change?
chromium
daylight / green to bluish green; incandescent / red to purplish red
Alexandrite color change
In what country was a large deposit of alexandrite discovered in the early 1980’s?
Brazil
What makes cat’s_eye chrysoberyl the most prized chatoyant gem?
excellent hardness; durability; the sharpest cat’s-eye
Why is cat’s_eye chrysoberyl marketed as a man’s gem?
it withstands rough wear and is subtly colored
The most economically important gem is ___________ .
tanzanite
In what area of Tanzania was tanzanite discovered?
Merelani
The name tanzanite was given to transparent blue zoisite by whom?
Tiffany & Co
Tanzanite’s best color is ___________ .
strongly saturated; blue or violetish blue
Almost all tanzanite is _______ .
treated
Untreated tanzanite is typically what color?
brownish
Tanavyte is a trade name for __________ .
purple synthetic YAG
In iolite; the most valuable main face_up color is ______ .
blue
Top color iolite is ____________ .
untreated
In what year was alexandrite first discovered?
1830
What color characteristic changes during alexandrite’s color_change effect?
hue
What color is top_quality alexandrite in daylight?
bluish green
The most prized chatoyant gem in the world is __________ .
cat’s_eye chrysoberyl
What country is the major source for cat’s_eye chrysoberyl?
Sri Lanka
Yellow to yellowish green through grayish green.
Cat’s_eye chrysoberyl
The color of fine quality cat’s_eye crysoberyl is ____________ .
semi transparent golden; yellow to slightly greenish yellow / brownish yellow “honey” color
What causes cat’s_eye chrysoberyl’s chatoyancy?
fine needle_like inclusions
What are the three factors related to the quality of cat’s_eye chrysoberyl?
bodycolor; transparency; quality of cutting
What does the trade term “milk and honey” mean with cat’s_eye chrysoberyl?
one side / original body color; other side / milky appearance.
Most gem tourmalines are __________ .
elbaites
Most gem tourmalines form in ___________ .
pegmatites
The world’s largest producer of gem_quality tourmaline is ______ .
Brazil
The most expensive variety of tourmaline is ________ .
Parabia
What trace element causes the color in Parabia?
copper
What is the trade term for blue tourmaline?
Indicolite
What country is the largest producer of chrome tourmaline?
Tanzania
Rubellite tourmaline is colored by what element?
manganese
How are many green and blue tourmalines lightened?
heating
What treatment is used for many Parabia tourmalines?
heat
What trace element causes the color of peridot?
iron
Where is the most of the world’s commercial_quality peridot mined?
Arizona
Blue zircon is colored by what treatment?
heat treatment
Metamict zircons are described as ____________ .
low zircons
Which countries produce the finest peridot?
Myanamar and Pakistan
What two groups of minerals share the same crystal structure but have slightly different chemical and physical properties.
tourmalines; garnets
Why do cutters have to fashion tourmalines in slender proportions?
elongated crystal growth
Why must cutters orient finished tourmaline gems carefully to achieve the best colors?
tourmalines strong plechroism
What country supplies the majority of the world’s gem_quality toumaline?
Brazil
What are the two most important tourmaline treatments?
heating; irradiation
What country has the main sources that supply the world with most of its LARGE fine_colored peridot?
Myanmar
What state in the US supplies the world with rough for much of its commercial_quality calibrated peridot?
Arizona
