Key Concepts Flashcards
Most Gems Are What?
Minerals
What Must a Mineral be to be a Gem?
Beautiful, Durable, and Rare
Are colored stone mining operations big or small?
Small
What effect can an appealing name have on a Gem?
makes it easier to sell
Changes that take place in a gems source country can do what to it?
effect it’s availability and price
What is the number one imported stone to the US by value?
Emerald
What are the raw materials of gemstone formation?
Rocks
What part of the earth do most colored stones form?
Crust
In igneous rocks what do large crystals indicate?
Slow cooling
In igneous rocks what do small crystals indicate?
Rapid cooling
What type of rock do some of the largest and most perfect gem crystals form?
Pegmatites
Thousands of tons of eroded rock might yield how much gem material?
Only a few ounces
are secondary deposits or primary deposits easier to work?
Secondary and may have greater concentration of gems
only tough gems survive to become part of primary or secondary deposits?
Secondary
How many crystal systems are crystalline minerals classified into
Seven
What does the exterior shape of a crystal often indicate?
It’s symmetry at an atomic level
When does twinning occur?
During crystal growth, or from cooling after the crystal has grown
What in a colored stone can help you figure out if it is natural, manmade, treated, or untreated
Inclusions
What determines a gems specific gravity
The atoms it’s made from
What are the terms for the three different ways a gem breaks?
Cleavage, parting, fracture
What determines a gems reaction to external stress?
It’s crystal structure
What is the most important factor to a colored stones desirability, marketability, and value?
Color
What is light?
A form of radiant energy that travels in waves
Visible light makes up what size portion of the electromagnetic spectrum?
Small
What combination of colors makes up white light? (6)
red, orange, yellow, green, blue, violet
What light effect causes most gem color?
Selective absorption, influenced by crystal structure
What causes most selective absorption related gem colors?
Interaction of electrons with visible light
What element causes the most desirable red and green gem colors?
Chromium
What element causes a greater variety of gem colors than any other transition element?
Iron
What can cause variations in color intensity in the same gem material?
Valence differences
Which is stronger colors produced by charge transfer or by dispersed ions?
Charge transfer
Can treatment alter or initiate some color-causing charge transfer reactions?
yes
The presence of transition elements adds new energy levels within a gems band gap, what does this do
Helps electrons absorb some visible light wavelengths
How does irradiation produce color in gems?
by creating color centers
Only what type of gems can be pleochroic?
Doubly refractive
Is dispersion greater in hi-RI gems or low-RI gems?
Hi-RI
Most synthetic gem crystals are produced by which two methods?
Melt or Solution
Pulling is important for which colored stone synthesis?
Sapphire, because it produces extremely pure, high quality crystals for tech and science applications
Which is slower and more expensive, solution processes or melt processes?
Solution
Which 6 gems are commonly heat treated?
Corrundum, tanzanite, zircon, topaz, aquamarine, and amber
How can heat treatments alter corundum?
Alter color and create or eliminate phenomena and inclusions
How can low temp heating improve appearance of ruby and pink sapphire?
By removing blue color zones
Is low temp or high temp heating harder to detect in corundum?
Low is harder to detect
How to produce blue color in geuda sapphire?
High temp heating in a reducing environment followed by relatively rapid cooling
When did quantities of lattice-diffusion treated corundum, feldspar, and spinel begin to enter the market?
2015
What care act can remote lattice diffusion with heavier elements like titanium and chromium
Polishing
A combo of beryllium diffusion and heat treatment does what to sapphires
Improves color in dark blue sapphires to make them more marketable
The color resulting from lattice diffusion with what element can penetrate the entire stone?
beryllium
What is the most common form of clarity enhancement?
Fracture filling
Today, how many emeralds are subject to clarity enhancement?
almost all
What two materials are often used for fracture filing?
Glass or resin
What terms are used for a gem that has a high proportion of filler
composites or manufactured
Is irradiated color always stable?
No
What can destroy irradiated color?
Heat or light
Which 3 gems are commonly irradiated?
Topaz, tourmaline, cultured pearl
Is bleaching common in pearl treatment?
yes
Which gem is commonly treated with a combo of bleaching and impregnation?
Jadeite
Which is one of the oldest gem treatments?
Dyeing
Which 4 gems are commonly dyed?
Cultured pearl, lapis lazuli, chalcedony, coral
Which country is the major source of colored stones
Africa
Which quality rough has the highest demand?
Mass-market-quality rough
What has industry consolidation led to
increasing dominance by larger companies
Where does the Chinese industry focus on exporting through?
Hong Kong
Who has become the global leader in the cutting and treatment of all types of colored stones?
Thailand
What percentage of all jewelry in the world is sold in the US?
About half
What year (decade) did auction houses become a major outlet for dealers’ high end stones?
Mid 1980s
What other stones should you judge a gemstones beauty and value off of?
Others of it’s own species or variety
In many gemstone species are pure hues or mixed hues more valued?
Pure hues
When can you use trade terms that imply a gem’s geographic origin
When you are sure of the source only
Cutting compromises that save weight often can cause which two issues
Extinction and/or windows
In general attractive colored stones tend to have what kind of hues and tones?
Highly saturated hues and medium to medium-dark tones
Stones with very light or very dark tone usually have issue reaching the same what as stones of medium tone
Saturation
Can larger stones appear more or less saturated than smaller stones cut from the same rough?
More
Do stones of large or small sizes typically reach fine color?
Both, depends on the stone type
True or false – transparent rough is usually faceted
TRUE
Is large expensive, rare, and high quality rough typically calibrated cuts?
No usually cut to retain as much weight as possible
What stage of cutting has the greatest potential effect on a finished gem’s value?
Preforming
What kind of gems are typically cut into cabochons, cameos, intaglios, or beads?
Opaque or translucent rough
Flat stones with shallow pavilions usually have areas of lower color intensity called what?
Windows
Most outline variations in colored stones are intended to do what?
Save weight
You’ll usually see dark areas or extinction through the crown in stones with what
Deep pavilions
Most proportion and symmetry variations are visible through the crown as what kind of brilliance?
reduced or uneven brilliance
What three things are the most important factors in evaluating a faceted gem’s proportions?
Crown and pavilion depths, symmetry of its profile, and it’s face-up outline
Clarity characteristics that effect which 3 things have the most influence on value?
Transparency, brilliance, or durability
What are the five factors that determine the influence of clarity characteristics on marketability?
nature, size, number, position, and relief
What is the highest colored stone clarity grade?
Eye-clean
Is it important for a colored stone buyer to be able to judge a gem’s quality with the unaided eye?
Yes, loupe the expensive ones though
Most colored stones are sold by what characteristic?
Weight
The sizes of calibrated gems in a parcel should be within what mm of each other?
0.10 mm
Which calibrated colored stone shapes are the biggest sellers?
Rounds and ovals
Which stone, when unheated, can command the highest per-carat price of all colored stones?
Ruby
What does Ruby rate on the Mohs hardness scale?
9
What are the most valuable ruby colors?
red to slightly purplish red with medium to medium dark tone and vivid saturation
What trace element in rubies causes them to be red and what else can it cause in ruby?
Chromium, can cause flourescence which intensifies bodycolor
What do the fines rubies form in?
Marble
Higher levels of what element in basalt-hosted rubies inhibits flourescence?
Iron
True or false – Everyone agrees on the division between ruby and pink sapphire
FALSE
How common is heat treatment in ruby?
Rubies are almost always heat treated to improve color and clarity
What secondary colors can low temp heat treatment remove from ruby to improve it’s color?
blue or brown secondary colors
True or false – High temp heat treatment can improve ruby clarity as well as it’s color?
TRUE
Is beryllium lattice diffusion easy or difficult to detect in ruby?
Difficult and often requires lab analysis
Is the clarity enhancement of a ruby stable?
No and a treated ruby’s appearance might change over time
Where is the world’s largest ruby cutting, treatment, and trading center?
Thailand
Where is the number one source of ruby in the world?
Africa
Which area has emerged as the world’s most important ruby source?
The montequez area of Mozambique
Which area was historically the world’s most important ruby source?
Mogok, Myanmar
Along with Thailand, where else are the world’s major ruby cutting and trading centers?
China, Sri Lanka, and India
Which two types of synthetic rubies have inclusions and growth structures that might closely resemble natural rubies?
Flux and hydrothermal
Use of the single word “sapphire” denotes what variety of corundum?
Blue
The most valuable sapphires have what color tone and saturation
velvety blue to violetish blue, medium to medium dark tones, strong to vivid saturation
What two trace elements can cause the blue of sapphire?
Iron and Titanium
Higher levels of what element make basalt related sapphires darker than non basaltic sapphires?
Iron
What trade term is what many consider the finest blue sapphire?
Kashmir
Is color zoneing common in sapphire?
yes
True or false – most blue sapphires are heat treated
TRUE
Where are most sapphires over 100 carats from?
Sri Lanka
What is the most common sapphire synthesis method?
Flame fusion
Who is the leading exporter of sapphire to the united states by volume and value?
Thailand
What percentage of all blue sapphires sold on the world market are sold to the US?
About half
What are Yogo Gulch sapphires characterized by?
Small size and saturated blue color and do not require heat treatment
Where is the major center of the corundum trade?
Thailand
Kashmir owes it’s sapphire reputation to a brief period of output in what year? (decade)
1880s
What elements cause most fancy sapphire colors?
Iron, titanium, and chromium
What kind of sapphires typically command the highest per-carat value
Padparadschas
Which fancy sapphires command almost as much value as padparadschas?
Fine Pink
True or false – Green sapphires are readily available and marketable
False, they are readily available but not marketable color
What is the typical corundum color change
blue or violet in daylight to violetish purple to strongly reddish purple in incandescent light
Which trace element causes sapphires color change?
Vanadium
What is the quality of the finest stars in star corundum?
distinct, centered, and uniform
what is the most valuable bodycolor in star corundum?
one that provides a strong contrast to the star
Which star curundum is the most valuable?
Star ruby
