GIA Colored Stones Assignment 21: Tanzanite, Iolite, Chrysoberyl, and Andalusite
pleochroic
Cat's-eye chrysoberyl is chatoyant and _____________.
light reflecting
Cat's-eye chrysoberyl's chatoyancy is caught by __________ _____________ from fine needle-like inclusions within the gemstone.
Tanzanite's toughness is fair to poor because...
...it has one direction of cleavage and is sensitive to thermal shock.
Brazil
A large deposit of alexandrite discovered in _____________ in the early 1980's briefly increased alexandrite's availability.
Tanavyte
A trade name for purple synthetic YAG is _____________. (synthetic alexandrite)
blue
About 5% of the tanzanite found is naturally _______.
50 cts
About _______ can be retrieved from each ton of Tanzanite rich earth that is moved.
pleochroic
Alexandrite is a _______________ gem. (green, orange, and purple-red)
8.5
Alexandrite is hard. ______ on the Mohs scale. (no cleavage)
1830
Alexandrite was discovered in ________.
1830
Alexandrite was first discovered in ________.
pleochroism
All the gems in this chapter share the optical property of _______________________.
heat-treated
Almost all tanzanite is...
standard
Although Russian alexandrite mines produce little today, the rare and vivid hues of Russian alexandrite still set the _____________ for fine color.
Brazil
Andalusite from ___________ shows the best hues. (dark green/rose-red)
chiastolite
Andalusite that occurs as an opaque material with a distinctive cross-shaped marking. (Greek "chiasma" or "crosspiece." / cross stone) (formed by carbon inclusions)(lower hardness than transparent bc of impurities)
yellowish green, orange
Andalusite's most prized colors are ______________ _______ and __________.
reds, greens, oranges
Andalusite's pleochroic colors tend towards ______, ____________, and ____________.
simultaneously
Andalusite's pleochroism is so pronounced that its hues are often visible ___________________ through the gem's crown, creating a mosaic effect.
man's gem
Because it withstands rough wear and is subtly colored, cat's-eye is traditionally marketed as a _________ ______.
supply
Because tanzanite comes from a single source, changes in ___________ drastically affect availability and prices
iolite
Cordierite is another name for ___________.
collector's gem
Currently, fine alexandrite is so scarce that it has virtually disappeared from the marketplace except as an expensive __________________ ________.
cat's-eye
Cymophane, a Greek word for "wavelike form" -- is an old name for _________-_______.
pleochroism
Due to tanzanite's strong ________________, cutters must balance weight retention against quality of face-up color.
chryosoberyl
Excellent hardness and durability combined with the sharpest cat's-eye make _______________ the most-prized chatoyant gem.
chrome tanzanite
Green zoisite is sometimes called...
yellow chrysoberyl
Known as "chrysolite" in the Victorian era.
blue
In iolite, the most valuable main face-up color is...
7
Iolate rates from ____ to 7.5 on the Mohs hardness scale but its toughness is only fair because it has distinct cleavage in one direction.
one-tenth
Iolite can be an affordable alternative to tanzanite because in comparable quality, it sells for about ______-__________ the price.
ion
Iolite comes from the Greek word for violet which is _____.
pleochroic
Iolite is a _______________ stone. (eye visible)
blue
Iolites with a predominantly _________ face-up color are more valuable, so cutters orient the finished stones to display the desirable color.
vanadium
Mint chrysoberyl is colored by...
precisely
Pleochroic and phenomenal gems must be ___________ oriented to display their optical effects properly.
tanzanite's best color
Strongly saturated blue or violetish blue is _______________ _________ __________.
forsterite
Synthetic _______________ is the most convincing tanzanite imitation to date.
6 to 7 Mohs
Tanzanite
orthorhombic
Tanzanite crystallizes in the ___________________ crystal system.
zoisite
Tanzanite is a transparent variety of...
heat treated
Tanzanite is almost always _______-__________ to bring out its more attractive blue and violet hues.
vanadium, heat
Tanzanite owes its intense blue color to the impurity element ____________ and _______ treatment
valence
Tanzanite turns blue because of a change in the ___________ state of the vanadium component when it is heated over 1100 degrees F.
1967
Tanzanite was discovered in...
promotion
Tanzanite's success in the marketplace was due in part to enthusiastic _____________.
best
The _______ tanzanite color is a strongly saturated pure blue or violetish blue
chromium
The color change in alexandrite is caused by....
Sri Lanka
The finest cat's eye deposits are in _____ __________.
Merelani
The first tanzanite was discovered in North Tanzania in __________.
viridine
The green variety of andalusite is called _____________.
cat's-eye chrysoberyl
The most-prized chatoyant gem in the world is...
Tiffany & Co.
The name tanzanite was given to transparent blue zoisite by...
Cat's-eye chrysoberyl
The only chatoyant gem mineral simply known as "cat's-eye" by gemologists is....
andalusite
This stone, discovered in Spain, is about a 7-7.5 on the Mohs scale.
untreated
Top-color iolite is...
chromium
Traces of ______________ cause alexandrite's color change.
treated
Unlike tanzanite, iolite is not __________.
brownish
Untreated tanzanite is typically...
rarely
Very ________ color change tanzanites have been found. (blue-violet in daylight, purple in incandescent light)
hue
What changes during alexandrite's color-change effect?
bluish green
What color is top-quality alexandrite in daylight?
chromium
What is responsible for the color-change effect in alexandrite?
iron
What is the transition element that causes iolite's violetish blue to violet color?
tanzanite
When blue sapphire is scarce _____________ offers an alternative.
marketable
When moderately priced commercial-quality blue sapphire is available, it's more _________________ than commercial-quality tanzanite.
Merelani
Where was tanzanite discovered?
Tanzanite
Which of the following gem's is most economically important?
Sri Lanka
Which of the following is a major source of cat's eye chrysoberyl?
Tiffany's
Who named tanzanite?
fine alexandrite
_________ ________________ is green to bluish green in daylight or fluorescent light and red to purplish red in incandescent light, with medium to medium-dark tone and moderately strong saturation.
color change
_____________ ___________ is the defining characteristic that distinguishes alexandrite from other chrysoberyl varieties.
alexandrite chysoberyl
______________ ______________ is the finest color-change gem, and the standard against which all other color-change gems are judged.
Tanzania
______________ is the only commercial source of gem-quality tanzanite.
the alexandrite effect
color-change phenomenon