Key Concepts and Terms Flashcards
(227 cards)
1
Q
A mass of tiny, randomly oriented crystals.
A
Aggregate
2
Q
A smooth, flat break in a gemstone parallel to planes of atomic weakness, caused by weak or fewer bonds between atoms, or both.
A
Cleavage
3
Q
A curved and ridged fracture in a gemstone, extending from the surface inward.
A
Conchoidal fracture
4
Q
An aggregate made up of individual crystals detectable only under very high magnification.
A
Cryptocrystalline
5
Q
How heavy an object is in relation to its size.
A
Density
6
Q
A gemstone’s ability to withstand wear, heat, and chemicals.
A
Durability
7
Q
Any break in a gem other than cleavage or parting.
A
Fracture
8
Q
The characteristic external crystal shape or form of a mineral.
A
Habit
9
Q
How well a gemstone resists scratches. Usually expressed in terms of the Mohs scale, with diamond the hardest (10) and talc the softest (1).
A
Hardness
10
Q
A characteristic enclosed within a gem- stone, or reaching its surface from the interior.
A
Inclusion
11
Q
Small pocket in a gem that’s filled with fluids and, sometimes, gas bubbles and tiny crystals. Usually created by environmental changes during crystal growth.
A
Liquid inclusion
12
Q
How well a gemstone resists breaking and chipping.
A
Toughness
13
Q
Atoms in a gem that aren’t part of its essential chemical composition.
A
Trace elements
14
Q
Change in a gem’s crystal direction during or after growth.
A
Twinning
15
Q
Location of a change in crystal growth direction.
A
Twinning plane
16
Q
A hollow cavity in a gem, usually filled with a liquid and a gas.
A
Two-phase inclusion
17
Q
The smallest group of atoms with both the characteristic chemical composition and crystal structure of a mineral.
A
Unit cell
18
Q
An aggregate made up of individual crystals visible under magnification.
A
Microcrystalline
19
Q
A flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane.
A
Parting
20
Q
Ratio of the weight of a material to the weight of an equal volume of water.
A
Specific gravity (SG)
21
Q
How well a gemstone resists light, heat, and chemicals.
A
Stability
22
Q
Damage caused by sudden, extreme temperature changes.
A
Thermal shock
23
Q
A hollow cavity in a gem, filled with a liquid, a gas, and one or more crystals.
A
Three-phase inclusion
24
Q
Crystalline minerals
A
are classified into seven crystal systems, depending on the symmetry of their unit cells.
25
The exterior shape of a crystal
often indicates its symmetry at an atomic level.
26
Some gems are rare because they require
rare chemical elements or unique geological conditions, or both, to form.
27
Twinning can result from a change
during crystal growth, or from cooling or pressure after the crystal has grown.
28
Inclusions in a colored stone
can help identify it as natural or manmade,untreatedor treated.
29
Large inclusions can
dramatically affect beauty, value, and durability.
30
Many rough gemstones
have recognizable crystal shapes that can help identify them.
31
The shapes and sizes of rough gem crystals
affect the shapes and sizes of finished stones.
32
A gem’s density and specific gravity
depend on the types of atoms it’s made of, and how closely they’re packed together.
33
The different ways a gem breaks
are called cleavage, parting, and fracture.
34
A gem’s crystal structure determines
its reaction to external stress.
35
Most gems are
minerals
36
To be a gem, a mineral must be
beautiful, durable, and rare.
37
Many colored stones are mined
by independent miners using small-scale mining methods.
38
An appealing name can make a gem
much easier to sell.
39
Changes that take place in a gem’s source country
can drastically affect its availability and price.
40
Treatments improve
the marketability and availability of many gems.
41
In spite of treatment that’s sometimes extensive,
emerald is the number one colored stone by value imported into the US.
42
Most consumers accept gem treatments
if they’re ethically disclosed and explained in a positive way.
43
Lacking a regular crystal structure.
Amorphous
44
The basic structural unit of all matter.
Atom
45
Kinds and relative quantities of atoms that make up a material.
Chemical composition
46
A substance that consists of atoms of only one kind.
Chemical element
47
Regular, repeating internal arrangement of atoms in a material.
Crystal structure
48
A broad gem category based on chemical composition and crystal structure.
Gem species
49
A subcategory of species, based on color, transparency, or phenomenon.
Gem variety
50
A family of gems from several closely related mineral species.
Group
51
Composed of, or arising from, non-living matter.
Inorganic
52
A natural, inorganic substance with a char- acteristic chemical composition and usually characteristic structure.
Mineral
53
Gems produced by natural processes, without human help.
Natural gems
54
Produced by, or derived from, a living organism.
Organic
55
A natural material composed of masses of mineral crystals of one or more kinds.
Rock
56
A mineral that contains the elements silicon and oxygen.
Silicate
57
Rocks are the raw materials of
gemstone formation.
58
Most colored stones form
in the earth’s continental crust.
59
Geological conditions during mountain building
are favorable for gem formation.
60
In igneous rocks, large crystals indicate
slow cooling, while small crystals indicate quick cooling.
61
Some types of volcanic rock
can transport existing gems from deep in the crust to the earth’s surface.
62
Some of the largest and most perfect gem crystals
come from pegmatites.
63
Superheated, pressurized water can
transfer minerals in solution and redeposit them in veins to form gems.
64
Mining economics are affected
by demand, political climate, labor costs, environment, accessibility, type of deposit, and mining methods.
65
An understanding of gemstone formation
helps prospectors pick the right places to look for gems.
66
Thousands of tons of rock may be eroded to yield only a few ounces of gem material.
may be eroded to yield only a few ounces of gem material.
67
Secondary deposits are easier to work than primary ones and might contain greater concentrations of gems.
easier to work than primary ones and might contain greater concentrations of gems.
68
Only the toughest gems survive to become part of secondary deposits.
survive to become part of secondary deposits.
69
A deposit where gems are eroded from their source rock, then transported away from the source and further concentrated.
Alluvial deposit
70
Localized changes caused by an igneous intrusion that takes place where the magma meets the surrounding rock. New minerals may form due to temperature changes or introduction of fluids from the magma.
Contact metamorphism
71
The earth’s innermost layer.
Core
72
The surface and outermost layer of the earth.
Crust
73
A deposit where gems are eroded from the source rock but remain in place close to the source.
Eluvial deposit
74
The wearing away and transport of rock materials by natural forces.
Erosion
75
A spherical, often hollow, mineral-lined cavity in rock.
Geode
76
Minerals dense enough to become concentrated and separated from lighter ones by the action of surface water.
Heavy minerals
77
Hot, high-pressure solution that can dissolve, transport, and deposit minerals from one place to another.
Hydrothermal fluid
78
Rock formed by the crystallization of molten material.
Igneous rock
79
Large mass of igneous rock that crystallizes underground without reaching the surface.
Intrusion
80
General term for any molten rock.
Magma
81
A layer between the earth’s crust and its core.
Mantle
82
Circulation in the mantle that drives the movement of the earth’s plates.
Mantle convection
83
Rock altered by heat and pressure, or by heated fluids from magma.
Metamorphic rock
84
An igneous rock formed from cooling, once-molten granite that follows fractures in its surrounding rock. It may contain very large crystals, and its shape is often thin and contorted.
Pegmatite
85
Workable alluvial deposit of gem minerals with economic potential.
Placer
86
A section of the earth’s rigid outer crust.
Plate
87
Study of the formation, structure, and
| movement of the plates of the earth’s crust.
Plate tectonics
88
Crystallization of minerals from a gas.
Pneumatolysis
89
Gems found in the rock that carried them to the surface.
Primary deposit
90
Changes in rock type and minerals over a wide area, caused by heat and pressure of large-scale geological events.
Regional metamorphism
91
A constant formation and recycling process that creates new rock from old.
Rock cycle
92
Gems found away from their primary source.
Secondary deposit
93
Rock produced from the eroded and weathered remains of existing rocks.
Sedimentary rock
94
A process that occurs when two of the earth’s plates collide, forcing one under the other.
Subduction
95
A mineral deposit that occupies an existing fissure or fracture in the rock.
Vein
96
Pertaining to igneous activity at the earth’s surface, where magma erupts through a volcano or a fissure.
Volcanic
97
A “foreign crystal” that formed in unrelated rocks and was brought to the surface as a passenger in magma.
Xenocryst
98
Color is the most important factor in determining a colored gemstone’s
desirability, marketability, and value.
99
Light is a form of energy that
travels in waves.
100
Most gemcolor is caused by selective absorption, which is influenced by
chemical composition and crystal structure.
101
Some colored gems can be identified by the way they
absorb visible light.
102
Because of differences in crystal structure, the same transition element can
cause different colors in different gems.
103
Chromium causes the most desirable
red and green gem colors.
104
Iron causes a greater variety of gem colors
than any other transition element.
105
Charge transfer is responsible for most
blue and yellow gem colors.
106
Treatment can alter or initiate some
color-causing charge transfer reactions.
107
Without exposure to natural or artificial radiation,
color centers can’t cause color in gems.
108
Only doubly refractive gems can be
pleochroic.
109
Interference produces either darkness
or the brightening of one or more colors.
110
Opal’s play-of-color is produced by the interaction of light with the gem’s microscopic internal structure of
stacked silica spheres.
111
Light reflecting from inclusions
causes several phenomenal effects in gems.
112
A pattern of dark vertical lines or bands shown by certain gems when viewed through a spectroscope.
Absorption spectrum
113
The cloudy bluish white light in a moonstone, caused by scattering of light.
Adularescence
114
A gem colored by trace elements in its crystal structure.
Allochromatic
115
Crossing of chatoyant bands, creating a star in the dome of a cabochon.
Asterism
116
A glittery effect caused by light reflecting from small, flat inclusions within a gemstone.
Aventurescence
117
A process where the electrons that selectively absorb light are passed back and forth between neighboring impurity ions.
Charge transfer
118
Bands of light in certain gems, caused by reflection of light from many parallel, needle-like inclusions or hollow tubes.
Chatoyancy
119
A small defect in the atomic structure of a material that can absorb light and give rise to a color.
Color center
120
A distinct change in gem color under different types of lighting.
Color change
121
A special kind of interference phenomenon that breaks up white light into its spectral hues.
Diffraction
122
When a gem’s crystal structure splits light into two rays that each travel at a slightly different speed and direction.
Double refraction
123
Emission of visible light by a material when it’s stimulated by ultraviolet radiation.
Fluorescence
124
A gem colored by an element that is an essential part of its chemical composition.
Idiochromatic
125
Interaction of two light rays traveling in the same path.
Interference
126
A process where two impurity atoms separated by another atom can still exchange electrons to selectively absorb light.
Intervalence charge transfer
127
A rainbow effect created when light is broken up into spectral hues by thin layers.
Iridescence
128
A broad flash of color in labradorite feldspar that disappears when the gem is moved.
Labradorescence
129
A two-toned effect seen when a chatoyant gem is positioned at right angles to a light source.
Milk and honey
130
Direction of single refraction in a doubly refractive gem.
Optic axis
131
Iridescence seen in some natural and cultured pearls and mother-of-pearl.
Orient
132
An unusual optical effect displayed by a gem.
Phenomenon
133
The flashing rainbow colors in opal.
Play-of-color
134
When a gem shows different body-
| colors from different crystal directions.
Pleochroism
135
Change in speed and possible change in direction of light as it travels from one material to another.
Refraction
136
Process by which a material absorbs some components of visible light and transmits others.
Selective absorption
137
When a gem’s crystal structure doesn’t change incoming light other than by refraction and absorption.
Single refraction
138
Elements that can selectively absorb some wavelengths of visible light and produce color in gems.
Transition elements
139
Knowing whether a gem is natural or synthetic is
crucial when buying or selling colored stones.
140
Imitations can be made of a variety of materials
including natural or synthetic versions of other gems.
141
The process used to produce a synthetic gem can
determine its value.
142
Most synthetic gem crystals are produced by either
a melt or a solution process.
143
Solution processes are generally
slower and more expensive than melt processes.
144
Solution processes can synthesize gems that closely
resemble natural gems.
145
Internal and external characteristics can help trained observers
separate natural from synthetic gems.
146
Gemologists play an important role in ensuring that disclosure
becomes the industry standard.
147
Two or more separate pieces of material joined to form a unit.
Assembled stone
148
A cylindrical synthetic crystal produced by the flame-fusion process.
Boule
149
A process in which finely ground powder is heated, sometimes under pressure, to produce a fine-grained solid material.
Ceramic process
150
Clearly and accurately informing customers about the nature of the goods they buy.
Disclosure
151
Two separate pieces of material fused or cemented together to form a single assembled stone.
Doublet
152
A process in which powdered chemi- cals are dropped through a high-temperature flame onto a rotating pedestal to produce a synthetic crystal.
Flame fusion
153
A melt process where a heating unit passes over a rotating solid rod of chemicals until it forms a synthetic crystal.
Floating zone
154
A process in which nutrients dissolve in heated chemicals, then cool to form synthetic crystals.
Flux growth
155
A process in which nutrients dissolve in a water solution at high temperature and pressure, then cool to form synthetic crystals.
Hydrothermal growth
156
Any material that looks like a natural gem and is used in its place.
Imitation gem
157
A synthetic-crystal growth method in which the chemical mixture is melted, then recrystallized.
Melt process
158
A process in which the synthetic crystal grows from a seed that is dipped into a chemical melt, then pulled away as it gathers material.
Pulling
159
A tiny crystal used as a template to control the size, speed, or direction of growth and the shape of a growing synthetic crystal.
Seed crystal
160
A synthetic-crystal growth method that uses cooling pipes around an interior of melted chemical ingredients.
Skull melt
161
A growth method in which the synthetic crystal grows from a dissolved chemical mixture, sometimes at high temperature and pressure.
Solution process
162
A synthetic-crystal growth method that starts without a seed crystal.
Spontaneous nucleation
163
A laboratory creation with essentially the same chemical composition, crystal structure, and properties as its natural counterpart.
Synthetic gem
164
A single assembled stone made from three separate pieces of material fused or cemented together, or from two pieces and a colored cement layer.
Triplet
165
Treatments that improve gem appearance and quality increase the supply of
commercially important gems.
166
Treatments that make gems more available and affordable are an important part of
today’s gem and jewelry market.
167
All treatments—even suspected or probable treatments
should be disclosed as part of every transaction.
168
Gems that are commonly heat treated include corundum, tanzanite, zircon, topaz, aquamarine, and amber.
aquamarine, and amber.
169
Heat treatment can alter color and create or eliminate
phenomena and inclusions.
170
Lattice diffusion with titanium produces a shallow layer of color
that can be removed with minor re polishing.
171
The color resulting from lattice diffusion with beryllium might
penetrate the entire stone.
172
Almost all emeralds on the market today are
fracture filled.
173
Irradiated color is not always stable, and exposure to heat or light can
destroy it.
174
Commonly irradiated gems include topaz, tourmaline, and
cultured pearl.
175
Bleaching is a fairly common
pearl treatment.
176
Jadeite is often treated with a combination of bleaching and
impregnation.
177
Dyeing is one of the
oldest gem treatments.
178
Commonly dyed gems include cultured pearl, lapis lazuli,
chalcedony, and coral.
179
A treatment that uses chemicals to lighten or remove color.
Bleaching
180
Filling of pores or other openings with melted wax, resin, polymer, or plastic to improve appearance and stability.
Colorless impregnation
181
A treatment that adds color or affects color by deepening it, making it more even, or changing it.
Dyeing
182
Using a filler to conceal fractures and improve the apparent clarity of a gem.
Fracture (fissure) filling
183
A chemical that treaters mix with some resins to cause them to solidify.
Hardener
184
Exposing a gem to rising tempera- tures for the purpose of changing its appearance.
Heat treatment
185
Exposing a gem to radiation to change or improve its color.
Irradiation
186
A treatment in which a gem is exposed to high temperatures and chemicals to allow penetration of color-causing elements.
Lattice diffusion
187
An oxygen-rich environment that surrounds a gem during heat treatment, causing it to absorb oxygen.
Oxidizing environment
188
A liquid filling material that’s very durable when it dries.
Polymer
189
A rapid heating and cooling process that produces fractures in a stone so it will accept dye.
Quench crackling
190
An oxygen-poor environment that surrounds a gem during heat treatment, causing it to lose oxygen.
Reducing environment
191
A clear, viscous substance that’s used to fill fractures in gemstones.
Resin
192
Heating a wrapped opal until smoke or ash penetrates its surface to darken it and bring out its play-of-color.
Smoke treatment
193
Soaking an opal in a hot sugar solution and then in sulfuric acid to darken it and bring out its play-of-color.
Sugar treatment
194
Altering a gem’s appearance by applying backings, coatings, or coloring agents like paint.
Surface modification
195
Any human-controlled process, beyond cutting and polishing, that improves the appearance, durability, or value of a gem.
Treatment
196
Different buyers require different goods to suit their customers’ needs.
customers’ needs.
197
The highest demand is for
mass-market-quality gem rough.
198
Many gems leave their source countries through
unofficial channels.
199
Stones pass through many hands before they reach the consumer, and there’s a
price increase at every step.
200
Many conditions threaten the stability of the
colored stone market.
201
Commercial-quality stones are generally
calibrated, and judged more by the price per stone than by their individual quality factors.
202
Cutting standards are generally looser for
low-end goods.
203
Color, cut, and clarity are important factors for
middle-market gems.
204
A parcel typically contains a range of qualities, and the best stones often sell for a
lot more than the remainder of the parcel.
205
Because retailers deal directly with consumers, they must have
complete confidence in their wholesalers.
206
Main attributes of a fine stone
rarity, exceptional color, and large size.
207
The documented origin of a fine-quality gem can be a powerful sales tool and have an impact
on its value.
208
Gemstone sizes cut to fit standard mountings.
Calibrated sizes
209
A document that indicates a stone’s geographic origin, based on its inclusions and trace element chemistry.
Certificate of origin
210
Market sector where average- quality gemstones are used in mass-market jewelry.
Commercial market
211
A unique piece designed and created for a particular customer, often around specially chosen stones.
Custom-made jewelry
212
A gem dealer’s term for a random sample from a parcel of gemstones, often used to assess the parcel’s overall quality.
Cut
213
A manufacturer who produces faceted stones, cabochons, or carvings.
Cutter
214
A city, region, or country with a large number of gemstone manufacturers.
Cutting center
215
Gemstone rough that’s transparent enough and of high enough quality to produce faceted gems.
Facet grade
216
Non-standard cutting, usually applied to large, important stones for use in expensive jewelry where standard size is not a consideration.
Free-size
217
A specific rough gemstone quality range, usually determined by color, size, clarity, and price.
Grade
218
Market sector where fine - quality, expensive gemstones are used in unique, handcrafted jewelry pieces.
High-end market
219
In mining terms, theft of a mine’s production by its workers.
High grading
220
A discounted price for buying an entire parcel or a substantial part of it.
Lot price
221
Market sector where better-quality gemstones are used in well-finished, moderately priced jewelry pieces.
Middlemarket
222
A mixture of gem qualities that represents unsorted production from a particular mine.
Mine lot (mine run)
223
The geographical place where a gem was mined.
Origin
224
A quantity of stones, sometimes of similar size and quality, perhaps from a single mine, but often from various sources, that’s offered for sale together.
Parcel
225
A premium price for selecting stones from a parcel.
Pick price
226
A gem-producing area, or a particular mine in that area.
Source
227
A company or individual that supplies gems to jewelry manufacturers and retailers.
Wholesaler
