GIA Colored Stones Exam 501-550 Flashcards
A synthetic crystal growth method in which the chemical mixture is melted; then recrystalized.
melt process
A synthetic crystal growth method that uses cooling pipes around an interior of melted chemical ingredients.
skull melt
A growth method in which the synthetic crystal grows from a dissolved chemical mixture; sometimes at high temperatures an pressure.
solution process
A synthetic growth method that starts WITHOUT a seed crystal.
spontaneous nucleation
Most synthetic gems are produced by either what two processes?
melt; solution
A mass of tiny; randomly oriented crystals.
aggregate
A smooth; flat break in a gemstone parallel to planes of atomic weakness; caused by weak or few bonds between atoms; or both.
cleavage
A curved and ridged fracture in a gemsotne; extending from the surface inward.
conchoidal fracture
An aggregate made up of individual crystals detectable only under very high magnification.
cryptocrystalline
How heavy an object is in relation to its size.
density
A gemstones ability to withstand wear; heat and chemicals.
durability
Any break in a gem other than cleavage or parting.
fracture
The characteristic external crystal shape or form of a mineral.
habit
How well a gemstone resists scratches. Usually expressed in terms of the Mohs scale; with diamond the harderst (10) and talc the softest (1).
hardness
An aggregate made up of individual crystals visable under magnification.
microcrystalline
A flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane.
parting
How well a gemstone resists light; heat; and chemicals is called ___________ .
stability
Ratio of the weight of a matrial to the weight of an equal volume of water.
specific gravity
Damage caused by sudden; extreme temperature changes.
thermal shock
A hollow cavity in a gem; filled with a liquid; a gas; and one or more crystals.
Three_phase inclusion
Atoms of a gem that aren’t part of its essential chemical composition.
trace element
Change in a gem’s crystal direction during or after growth.
twinning
Location of a change in crystal growth direction.
twinning plane
A hollow cavity in a gem; usually filled with a liquid AND a gas.
Two_phase inclusion
The smallest group of atoms with both the characteristic chemical composition and crystal structure of a mineral.
unit cell
A unit cell defines a mineral’s ___________ .
basic identity
If a crystal grows in a flux that is highly saturated with the necessary elements it tends to be ___________ .
small
What aggregate’s crystals are visible only with magnification greater than a standard gemological microscope?
cryptocrystalline
Which is classified in the orthorhobic system? A. Beryl B. Topaz C. Garnet D. Corundum
B. Topaz
Which element causes the red in ruby and the green in emerald?
chromium
What type of twinning is caused by enviromental change after the gem forms?
polysynthetic
What type of twinning looks as if two crystal halves are mirror images?
contact
Needles of actinolite found in emerald are classified as what?
inclusions
A two_phase inclusion is a cavity in a gem that’s typically filled with a ___________ and a __________ .
liquid and gas
Atoms in a gem that are not part of its essential chemical composition are called what?
trace elements
The trace elements that cause corundum’s blue are ____________ and ________ .
iron and titanium
An object’s weight in relation to its size is called its ____________ .
density
Which gems are cryptocrystalline? A. opal and amethyst B. nephrite and jadeite C. chalcedony and turquoise
C. chalcedony and turquoise
Rough spinel often occurs as what type of crystals?
twinned
Many fashioned rubies have shallow proportions because they’re cut from what type of crystals?
flat
What are the three different ways a gem can break?
cleavage and parting and fracture
A gem’s price divided by its carat weight is called ___________ .
per_carat price
The international unit of measurement for gem weight is the _________ .
metric carat
Individual stone prices are referred to as __________ .
unit prices
How many points are in a metric carat?
100
A metric carat equals __________ gram(s).
0.20 gram
How are most colored stones sold?
by weight
What category of colored stone is often sold per piece?
small; inexpensive
Sieves are most useful for sorting round gems with diameters that are what size?
3mm and below
When you first start to count a large pile of small gems; it’s best to seperate them into groups of how many?
5
