GIA Colored Stones Exam 51-100 Flashcards
The lapis lazuli trade grade that’s often spotted with green and shows obvious calcite is called ________ .
Chilean
The finest color of turquoise is ______________ .
Intense medium blue
The purest blue colors of turquoise are caused by _________ .
copper
What is the trade term for top_color turquoise?
Persian
Turquoise usually forms in __________ .
Limonite
What is the color of the markings that sandstone matrix creates in turquoise?
tan
Stabalized turquoise is a tade term for what?
Polymer_impregnated turquoise
A new turquoise treatment that appeared in the 1980’s and has been used to treat more thabn 10 million carats is _____________ .
Zachary method
The major source of turquoise today is ___________ .
Southwestern US.
Reconstructed turquoise is __________ .
Immitation
Malachite’s color is caused by what element?
Copper
The only commercial source of charolite is in what country/
Russia
Chalcedony with curved or irregular bands or layers that differ in color and transparency.
Agate
A crystal growth habit with a bumpy appearance similar to a bunch of grapes.
Botryodal
A cryptocrystalline quartz aggregate.
Chalcedony
A property of some crystals that causes them to vibrate at a constant frequency when subjected to an electrical current.
Piezoelectricity
A type of sagenitic quartz containing needle_like rutile inclusions.
Rutilated quartz
A transparent quartz; usually rock crystal; that contains eye_visable inclusions; often named according to the type of inclusions it contains.
Sagenitic
A table_cut gem with a flat or slightly domed top and sometimes a carved design; typically set in men’s rings and cufflinks.
Signet
A type of sagenitic quartz containing needle_like or rod_like tourmaline inclusions.
Tourmalated quartz
Cryptocrystalline quartz is known as ___________ .
Chalcedony
Chalcedony with curved or irregular bands or layers that differ in color and transparency is known as ________ .
Agate
What type of crystalline has the smallest crystal size?
Cryptocrystalline
In the nineteenth century; a major source of amethyst was discovered in what country?
Brazil
The color of amethyst results from __________________ .
Color centers acting on iron .
One of amethyst’s finest colors is _____________________ .
medium_dark strong reddish purple.
What country is the major source for commercial_quality amethyst?
Brazil
Maraba amethyst is often
Uniform in color
What treatment lightens dark amethyst?
heat
How is most of the citrine on the market produced?
By heating amethyst
What country is the source for natural ametrine?
Bolivia
What type of aggregate is tiger’s eye quartz?
microcrystalline
Multiple slender crystals or channels cause this in cat’s_eye chacelony.
Chatoyancy
What is the color of chrysoprase?
Yellowish green
Treated black chalcedony is also known by the trade term ____________ .
Black onyx
The trade considers what gemstone to have the finest green among the colored stones?
Emerald
When all factors are equal; a great difference in emerald value can be caused by slight differences in __________; ____________ and ____________ .
hue; tone and saturation.
Emerald’s color_causing trace elements are _________ ; __________ and ___________ .
Chromium; Vanadium; Iron
What can cause a great reduction in a finished emerald’s value?
Poor cutting
The trade accepts the fact that most emeralds contain _____________ .
Eye visable inclusions
Inclusions that make an emerald less valuable also make it less _____________ .
Transparent.
How are emerald’s fractures usually filled?
Oil; Resin; Both
What type of emerald commands premium prices?
Untreated
What is the safest way to clean emeralds?
Gentle scrubbing with warm soapy water.
What two countries account for 75% of emerald purchases worldwide?
The US and Japan.
What four countries provide most of the world’s emeralds?
Brazil; Columbia; Zambia; Zimbabwe
The world’s emeralds are judged by what country’s finest?
Columbia
What country’s emerald mines have fewer fractures than emeralds from other sources?
Africa
What is the most common emerald imitation used in jewelry?
Synthetic spinel triplets
What two methods are used to synthesize emeralds?
Flux and hydrothermal
