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