Key Concepts Flashcards
1
Q
Most Gems Are What?
A
Minerals
2
Q
What Must a Mineral be to be a Gem?
A
Beautiful, Durable, and Rare
3
Q
Are colored stone mining operations big or small?
A
Small
4
Q
What effect can an appealing name have on a Gem?
A
makes it easier to sell
5
Q
Changes that take place in a gems source country can do what to it?
A
effect it’s availability and price
6
Q
What is the number one imported stone to the US by value?
A
Emerald
7
Q
What are the raw materials of gemstone formation?
A
Rocks
8
Q
What part of the earth do most colored stones form?
A
Crust
9
Q
In igneous rocks what do large crystals indicate?
A
Slow cooling
10
Q
In igneous rocks what do small crystals indicate?
A
Rapid cooling
11
Q
What type of rock do some of the largest and most perfect gem crystals form?
A
Pegmatites
12
Q
Thousands of tons of eroded rock might yield how much gem material?
A
Only a few ounces
13
Q
are secondary deposits or primary deposits easier to work?
A
Secondary and may have greater concentration of gems
14
Q
only tough gems survive to become part of primary or secondary deposits?
A
Secondary
15
Q
How many crystal systems are crystalline minerals classified into
A
Seven
16
Q
What does the exterior shape of a crystal often indicate?
A
It’s symmetry at an atomic level
17
Q
When does twinning occur?
A
During crystal growth, or from cooling after the crystal has grown
18
Q
What in a colored stone can help you figure out if it is natural, manmade, treated, or untreated
A
Inclusions
19
Q
What determines a gems specific gravity
A
The atoms it’s made from
20
Q
What are the terms for the three different ways a gem breaks?
A
Cleavage, parting, fracture
21
Q
What determines a gems reaction to external stress?
A
It’s crystal structure
22
Q
What is the most important factor to a colored stones desirability, marketability, and value?
A
Color
23
Q
What is light?
A
A form of radiant energy that travels in waves
24
Q
Visible light makes up what size portion of the electromagnetic spectrum?
A
Small
25
What combination of colors makes up white light? (6)
red, orange, yellow, green, blue, violet
26
What light effect causes most gem color?
Selective absorption, influenced by crystal structure
27
What causes most selective absorption related gem colors?
Interaction of electrons with visible light
28
What element causes the most desirable red and green gem colors?
Chromium
29
What element causes a greater variety of gem colors than any other transition element?
Iron
30
What can cause variations in color intensity in the same gem material?
Valence differences
31
Which is stronger colors produced by charge transfer or by dispersed ions?
Charge transfer
32
Can treatment alter or initiate some color-causing charge transfer reactions?
yes
33
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
34
How does irradiation produce color in gems?
by creating color centers
35
Only what type of gems can be pleochroic?
Doubly refractive
36
Is dispersion greater in hi-RI gems or low-RI gems?
Hi-RI
37
Most synthetic gem crystals are produced by which two methods?
Melt or Solution
38
Pulling is important for which colored stone synthesis?
Sapphire, because it produces extremely pure, high quality crystals for tech and science applications
39
Which is slower and more expensive, solution processes or melt processes?
Solution
40
Which 6 gems are commonly heat treated?
Corrundum, tanzanite, zircon, topaz, aquamarine, and amber
41
How can heat treatments alter corundum?
Alter color and create or eliminate phenomena and inclusions
42
How can low temp heating improve appearance of ruby and pink sapphire?
By removing blue color zones
43
Is low temp or high temp heating harder to detect in corundum?
Low is harder to detect
44
How to produce blue color in geuda sapphire?
High temp heating in a reducing environment followed by relatively rapid cooling
45
When did quantities of lattice-diffusion treated corundum, feldspar, and spinel begin to enter the market?
2015
46
What care act can remote lattice diffusion with heavier elements like titanium and chromium
Polishing
47
A combo of beryllium diffusion and heat treatment does what to sapphires
Improves color in dark blue sapphires to make them more marketable
48
The color resulting from lattice diffusion with what element can penetrate the entire stone?
beryllium
49
What is the most common form of clarity enhancement?
Fracture filling
50
Today, how many emeralds are subject to clarity enhancement?
almost all
51
What two materials are often used for fracture filing?
Glass or resin
52
What terms are used for a gem that has a high proportion of filler
composites or manufactured
53
Is irradiated color always stable?
No
54
What can destroy irradiated color?
Heat or light
55
Which 3 gems are commonly irradiated?
Topaz, tourmaline, cultured pearl
56
Is bleaching common in pearl treatment?
yes
57
Which gem is commonly treated with a combo of bleaching and impregnation?
Jadeite
58
Which is one of the oldest gem treatments?
Dyeing
59
Which 4 gems are commonly dyed?
Cultured pearl, lapis lazuli, chalcedony, coral
60
Which country is the major source of colored stones
Africa
61
Which quality rough has the highest demand?
Mass-market-quality rough
62
What has industry consolidation led to
increasing dominance by larger companies
63
Where does the Chinese industry focus on exporting through?
Hong Kong
64
Who has become the global leader in the cutting and treatment of all types of colored stones?
Thailand
65
What percentage of all jewelry in the world is sold in the US?
About half
66
What year (decade) did auction houses become a major outlet for dealers' high end stones?
Mid 1980s
67
What other stones should you judge a gemstones beauty and value off of?
Others of it's own species or variety
68
In many gemstone species are pure hues or mixed hues more valued?
Pure hues
69
When can you use trade terms that imply a gem's geographic origin
When you are sure of the source only
70
Cutting compromises that save weight often can cause which two issues
Extinction and/or windows
71
In general attractive colored stones tend to have what kind of hues and tones?
Highly saturated hues and medium to medium-dark tones
72
Stones with very light or very dark tone usually have issue reaching the same what as stones of medium tone
Saturation
73
Can larger stones appear more or less saturated than smaller stones cut from the same rough?
More
74
Do stones of large or small sizes typically reach fine color?
Both, depends on the stone type
75
True or false – transparent rough is usually faceted
TRUE
76
Is large expensive, rare, and high quality rough typically calibrated cuts?
No usually cut to retain as much weight as possible
77
What stage of cutting has the greatest potential effect on a finished gem's value?
Preforming
78
What kind of gems are typically cut into cabochons, cameos, intaglios, or beads?
Opaque or translucent rough
79
Flat stones with shallow pavilions usually have areas of lower color intensity called what?
Windows
80
Most outline variations in colored stones are intended to do what?
Save weight
81
You'll usually see dark areas or extinction through the crown in stones with what
Deep pavilions
82
Most proportion and symmetry variations are visible through the crown as what kind of brilliance?
reduced or uneven brilliance
83
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
84
Clarity characteristics that effect which 3 things have the most influence on value?
Transparency, brilliance, or durability
85
What are the five factors that determine the influence of clarity characteristics on marketability?
nature, size, number, position, and relief
86
What is the highest colored stone clarity grade?
Eye-clean
87
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
88
Most colored stones are sold by what characteristic?
Weight
89
The sizes of calibrated gems in a parcel should be within what mm of each other?
0.10 mm
90
Which calibrated colored stone shapes are the biggest sellers?
Rounds and ovals
91
Which stone, when unheated, can command the highest per-carat price of all colored stones?
Ruby
92
What does Ruby rate on the Mohs hardness scale?
9
93
What are the most valuable ruby colors?
red to slightly purplish red with medium to medium dark tone and vivid saturation
94
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
95
What do the fines rubies form in?
Marble
96
Higher levels of what element in basalt-hosted rubies inhibits flourescence?
Iron
97
True or false – Everyone agrees on the division between ruby and pink sapphire
FALSE
98
How common is heat treatment in ruby?
Rubies are almost always heat treated to improve color and clarity
99
What secondary colors can low temp heat treatment remove from ruby to improve it's color?
blue or brown secondary colors
100
True or false – High temp heat treatment can improve ruby clarity as well as it's color?
TRUE
101
Is beryllium lattice diffusion easy or difficult to detect in ruby?
Difficult and often requires lab analysis
102
Is the clarity enhancement of a ruby stable?
No and a treated ruby's appearance might change over time
103
Where is the world's largest ruby cutting, treatment, and trading center?
Thailand
104
Where is the number one source of ruby in the world?
Africa
105
Which area has emerged as the world's most important ruby source?
The montequez area of Mozambique
106
Which area was historically the world's most important ruby source?
Mogok, Myanmar
107
Along with Thailand, where else are the world's major ruby cutting and trading centers?
China, Sri Lanka, and India
108
Which two types of synthetic rubies have inclusions and growth structures that might closely resemble natural rubies?
Flux and hydrothermal
109
Use of the single word “sapphire” denotes what variety of corundum?
Blue
110
The most valuable sapphires have what color tone and saturation
velvety blue to violetish blue, medium to medium dark tones, strong to vivid saturation
111
What two trace elements can cause the blue of sapphire?
Iron and Titanium
112
Higher levels of what element make basalt related sapphires darker than non basaltic sapphires?
Iron
113
What trade term is what many consider the finest blue sapphire?
Kashmir
114
Is color zoneing common in sapphire?
yes
115
True or false – most blue sapphires are heat treated
TRUE
116
Where are most sapphires over 100 carats from?
Sri Lanka
117
What is the most common sapphire synthesis method?
Flame fusion
118
Who is the leading exporter of sapphire to the united states by volume and value?
Thailand
119
What percentage of all blue sapphires sold on the world market are sold to the US?
About half
120
What are Yogo Gulch sapphires characterized by?
Small size and saturated blue color and do not require heat treatment
121
Where is the major center of the corundum trade?
Thailand
122
Kashmir owes it's sapphire reputation to a brief period of output in what year? (decade)
1880s
123
What elements cause most fancy sapphire colors?
Iron, titanium, and chromium
124
What kind of sapphires typically command the highest per-carat value
Padparadschas
125
Which fancy sapphires command almost as much value as padparadschas?
Fine Pink
126
True or false – Green sapphires are readily available and marketable
False, they are readily available but not marketable color
127
What is the typical corundum color change
blue or violet in daylight to violetish purple to strongly reddish purple in incandescent light
128
Which trace element causes sapphires color change?
Vanadium
129
What is the quality of the finest stars in star corundum?
distinct, centered, and uniform
130
what is the most valuable bodycolor in star corundum?
one that provides a strong contrast to the star
131
Which star curundum is the most valuable?
Star ruby
132
Between star sapphire and star ruby with all other factors being equal which would bring a higher price?
Star ruby
133
Which country produces the widest range of fancy sapphire colors in the world?
Sri Lanka
134
Who is a major source of pink sapphire?
Madagascar
135
True or false purple sapphires are often heat treated
True – to achieve a more valuable pink or red hue
136
Beryllium diffusion of sapphire can produce which colors?
Padparadscha, as well as highly saturated yellows and oranges
137
Which stone has the finest green among colored stones?
Emerald
138
What are the most desirable emerald colors?
bluish green to green, with strong to vivid saturation and medium to medium dark tone
139
What trace elements influence emerald's color?
Chromium, vandium, and iron
140
What level of inclusions does the trade typically accept in emerald?
Eye-visible
141
What type of inclusions have a strong negative effect on emerald value?
Inclusions that reduce transparency or that are highly visible
142
What is emerald often fracture filled with?
Oil, resin, or a mixture of both
143
What is the safest way to clean emeralds?
Gentle scrubbing with warm, soapy water
144
True or false – emerald is primarily mined from secondary sources
False, emerald is usually mined from primary hard rock sources
145
What percentage of Colombia's emeralds have already been mined according to government geological surveys
20.00%
146
Which areas do most facet grade emerald mined in Brazil come from?
The Itabira, Nova Era, and Capoeirana areas
147
Zambia's Kagem mine produces what estimated percent of the world's emerald supply?
20.00%
148
Who is the global leader in cutting of Zambian emeralds?
Jaipur, India
149
True or false – Colombia and Brazil cut most of their lower quality material and send the higher quality to India to be cut
False, they cut their better quality emerald and send the lower quality to Jaipur, India
150
Who is the number one supplier of emerald to the US in terms of total carats and who in terms of value?
India in terms of total carats Colombia in terms of value
151
Who is the number one exporter of emerald to the US in terms of per-carat price?
Switzerland
152
Describe natural pearl formation
A foreign object gets inside a pearl-bearing mollusk's shell and irritates its soft tissue
153
What three things contributed to the decline of the pearl industry?
Culturing, plastic buttons, and oil drilling
154
What is the key difference between saltwater and freshwater pearl culturing?
Saltwater – gonad, Freshwater – mantle (in terms of where bead is planted)
155
What are the four major types of cultured whole pearls?
| What are the four major types of cultured whole pearls?
Akoya, South Sea, Tahitian, and Freshwater
156
What does it mean to say most Chinese freshwater cultured pearls are mantle nucleated?
They are non-beaded
157
Who produces the overwhelming majority of the world's freshwater cultured pearls?
China
158
What are the two important selling points for cultured pearls?
Versatility and timeless appeal
159
What provides a common language for evaluating pearls?
The GIA pearl description system
160
True or false – all pearls are evaluated from the same factors
False – Each value factor varies in importance for different pearl types
161
What is the one factor of larger pearls that makes them more valuable?
Their rarity
162
What is the rarest and most valuable cultured pearl shape?
Round
163
What happens to value as a pearls shape gets farther away from round?
It gets less valuable
164
Do all pearls display bodycolor? And do all pearls have overtone/orient?
All pearls have bodycolor, some display overtone or orient or both
165
What two factors contribute to improving a pearls luster during growth?
Cool water and a clean environment
166
How common is it for pearls to be completely free of blemishes?
Uncommon, very few pearls are
167
What must any cultured pearl of significant value have?
Acceptable nacre quality
168
What are jadeite's three most important qualities?
Color, transparency, texture
169
What is the most valuable jadeite?
Imperial intense green
170
In addition to green what other colors can jadeite be?
Lavender, red, orange, yellow, brown, white, black, or gray
171
What are the qualities of the most valuable jadeite's color?
Evenly distributed, uniform, strong
172
True or false jadeite is very tough
True, it's toughness is exceptional
173
Where is the main polishing center for jadeite from around the world?
China
174
What does asia use to describe the extent of jade treatment?
Type A, B, and C
175
Between jadeite and nephrite which is more resistant to fracturing and why?
Nephrite, interlocking fibrous structure makes it more resistant to fracturing
176
What is the most sought after nephrite color?
White
177
What are the 2 most common jade imitations today?
Glass and plastic
178
What does precious opal's internal structure consist of?
An orderly arrangement of uniform, submicroscopic silica spheres
179
What is play of color in opal produced by?
Diffraction of white light when it interacts with precious opal's orderly internal structure
180
True or false, scientists know how opal is formed
False, scientists have proposed many different opal formation theories
181
What are opal types based off of?
Background color
182
Which types of opals command the highest prices of all opal types?
Black opals
183
Which opal type makes up the bulk of the commercial quality opal on the market?
White
184
What effect does matrix backing have on boulder opal?
Makes it more durable than other opal types
185
What is the bodycolor of the most valuable fire opals?
uniform red-orange to bright red color
186
Which opal type is most commonly faceted?
Fire opal
187
What three factors contribute to an opal's unique beauty?
Color, patter, clarity
188
True or false – the rarest play of color contains hues that range across the entire spectrum
TRUE
189
What color is often considered the most desireable play of color hue?
Red
190
Do opal experts prefer patterns of large or small color patches?
Large, closely arranged color patches
191
What is the opal cutter's main goal?
Maximize play of color
192
Which three countries are the worlds most important opal suppliers?
Australia, Ethiopia, and Mexico
193
Which kinds of opal deposits does Australia have
Black, White, Crystal, and Boulder Opal
194
Where is the world's main source of fine-quality black opal?
New South Wales town of Lightning Ridge
195
Where is the worlds main source of boulder opal?
Australian state of Queensland
196
Opals mined in Ethiopia are all of what kind of origin?
Volcanic
197
Who is the world's major source of fire opal?
Mexico
198
Who are the two major developing markets for opal?
China, and India
199
Who is the major cutting center for Ethiopian opal?
Jaipur, India
200
Quartz varieties differ mostly in the size of their what?
Crystals
201
How are many gem quality quartz varieties treated?
Heated, bleached, or dyed
202
Is chalcedony considered by the gem trade to be a separate or same species from large crystal quartz varieties?
separate species
203
What qualities make amethyst one of the most popular colored gemstones?
Availability, affordable price, and attractive color
204
What is the most desireable color qualities of the finest amethysts?
Strongly saturated, medium dark to dark reddish purple or purple, with no visible color zoning
205
Amethyst is sold in a variety of grades based many on what?
Color
206
Whose amethyst often retains its deep color even in small sizes?
Zambian
207
Who is the world's major source of commercial quality amethyst?
Brazil
208
Describe the finest citrine color
saturated yellow to reddish orange, free of brownish tints
209
How is most citrine on the market produced?
By heat treatment of amethyst
210
Why are smoky quartz crystals ideal for gem carvers and sculptors?
They're large, inexpensive, and free from flaws
211
What was one of the first gems to be fashioned and how long has it been used in jewelry?
Chalcedony, 3,000 years
212
Describe the finest chrysoprase color
light to medium yellowish green
213
What is one of the most valuable chalcedony varieties?
Chrysocolla-in-chalcedony
214
What is treated black chalcedony better known as?
Black onyx
215
What do collectors often give agates names based off of?
Their appearance
216
What contributed to tanzanite's success in the marketplace?
Enthusiastic promotion
217
Describe the finest tanzanite color
Strongly saturated pure blue or violetish blue
218
Does tanzanite display pleochroism?
Yes, strong, cutters must factor in
219
How common is it to heat tanzanite?
Almost always heated to bring out blue and violet hues
220
Who is the only commercial source of gem quality tanzanite?
Tanzania
221
Which stone is more marketable than commercial quality tanzanite?
Blue sapphire
222
What is the most convincing tanzanite imitation to date?
Synthetic fosterite
223
What is the most valuable color of Iolite?
Blue face up color
224
What stone can iolite be a substute for and what is the price difference?
Tanzanite, about 1/10 the price
225
What is the finest color change gem?
Alexanderite chrysoberyl
226
What trace element causes alexandrite's color change?
Chromium
227
What is the finest color range for Alexandrite in both colors?
bluish green in daylight or flourescent light and red to purplish red in incandescent light with medium to medium dark tone and moderately strong saturation
228
What level of output do Russian alexandrite mines see today?
Very little
229
In the early 1980s where was a large deposit of alexandrite discovered?
Brazil
230
True or false, alexandrite is so scarce that it has virtually dissapeared from the gem marketplace
True, except as an expensive collector's gem
231
What makes cat's eye chrysoberyl the most prized chatoyant gem?
Excellent hardness and durability combined with the sharpest cat's eye
232
What causes the cat's eye chrysoberyl's chatoyancy
Light reflecting from fine needle like inclusions within the gemstone
233
Why is cat's eye traditionally marketed as a man's gem?
It withstands rough wear and is subtly colored
234
Which topaz varities are the most rare and valuable?
Red and pink, including imperial topaz
235
What are the two causes of the wide variety of colors in topaz?
Chromium and color centers
236
Why is topaz often cut as long ovals, pears, or emerald cuts?
Because many topaz crystals are elongated
237
Why does topaz require special care in cutting, polishing, mounting, and wear
Because of it's cleavage
238
True or false – the definitions of imperial topaz can vary widely
TRUE
239
What color is most common for natural topaz?
Colorless, but treatment can produce a blue color
240
Where is the world's major commercial source of imperial and red topaz?
Ouro Preto, Brazil
241
Topaz treatments commonly involve heating or a combination of heating and what?
Irradiation
242
If yellow to reddish brown topaz contains chromium, careful heat treatment can produce what color?
Pink
243
What color is finest for aqua marine?
moderately strong medium dark blue to slightly greenish blue
244
Does aqua marine generally show its finest most saturated color is large or small sizes?
Large
245
Which 3 countries are the leading producers of aquamarine?
Brazil, Pakistan, and China
246
Virtually all aquamarine is heat treated to remove which color component?
Yellow to produce more marketable blue
247
Morganite is almost heated, or irradiated first then heated, to produce or improve what color?
Pink
248
Traces of what cause red beryl's color?
Manganese
249
What is the world's only known source of red beryl?
Utah, US
250
What distinguishes green beryl from emerald?
Tone and saturation levels
251
What are tourmalines?
A group of minerals that share the same crystal structure but have slightly different chemical and physical properties
252
most gem tourmalines are elbaites that form in what?
Pegmatites
253
True or false fashioned tourmalines are more valuable than well formed fine color uncut tourmaline crystals
False, some well formed fine color tourmaline crystals are more valuable as mineral specimens
254
The shapes of many tourmaline crystals often force cutters to fashion gems with what kind of proportions?
Slender
255
Does tourmaline have strong pleochroism?
Yes
256
Who supplies the majority of the world's gem quality tourmaline?
Brazil
257
Which two areas in Africa are the most economically important tourmaline sources?
Nigeria and Mozambique
258
Traces of what cause Paraiba tourmaline's extraordinary colors?
Copper
259
What are the two most important tourmaline treatments?
Heating and irradiation
260
Why is peridot best cleaned with warm water and mild detergent or soap?
It is sensitive to rapid temperature changes and chemicals
261
Who supplies the marjoty of the world's large fine color peridot?
Myanmar
262
Who supplies the world with rough for much of it's commercial calibrated preidot?
Arizona, US
263
What does zircon need care in handling and wear?
Brittleness
264
True or false, virtually all blue and colorless zircons have been treated
TRUE
265
True or false, virtually all garnet and spinel are treated?
False, they are rarely treated
266
Are garnet and spinel singly or doubly refractive and what does this mean for cutters?
Singly, no need for cutters to consider pleochroism
267
Garnets belong to a group of (blank) with the same (blank blank) but slightly different (blank blank)
Minerals, Crystal structure, chemical composition
268
Many garnets are a mixture of two or more (blank) species
Garnet
269
Gemologists classify garnets based on what, and what do dealers sell garnets based off?
Physical and optical properties, color and/or origin
270
Is small tsavorite rough more rare than large tsavorite rough?
No, large tsavorite rough is extremely rare
271
What chemical gives tsavorite it's color?
Vanadium
272
What is the ideal fine color for tsavorite?
pure green or green with a slight amount of blue
273
Where is tsavorite mostly mined?
East Africa
274
What variety of andradite is demantoid?
The transparent green variety
275
What elements color demantoid?
A mixture of chromium and iron
276
Demantoid comes mostly from which two places?
Russia and Africa
277
What keeps demantoid's prices high?
Inconsistent supply and continuing demand
278
New discoveries of spessartine in what year made it much more available?
1880s
279
Spessartine is the most valuable what color garnet?
Orange
280
Hessonite is what colored variety of the grossular species?
transparent orange to cinnamon colored
281
Most red garnets, including the popular rhodolite, are mixtures of what 2
Pyrope and almandine
282
What is the most valuable garnet?
Rhodolite
283
What is the ideal color for rhodolite?
dark purplish red to light reddish purple
284
What has been the most important source of rhodolite since the 1960s
East Africa
285
Huge numbers of these dark toned, reddish brown, calibrated garnets are used in inexpensive mass market jewelry
Pyrope-almandine
286
Color change garnets are usually what kind?
Pryope-spessartine mixtures
287
What is the usual color change agent in garnet?
Vanadium
288
What makes the red hue in spinnel stronger?
The higher the chromium content the stronger the red hue
289
What is the most rare and valuable spinel hue?
Red
290
Spinel forms in the same what kind of rocks as corundum?
Metamorphic
291
You may find spinel and corundum in the same what kind of deposit?
Alluvial
292
True or false, because spinel is rare and synthetic spinel is common, many people have never seen the natural stone
TRUE
293
The presence of what produces lapis lazuli's prized royal blue color?
Lazurite
294
Lapis value is based on color and the presence or absence of which two things?
Calcite or Pyrite
295
What country is the world's major source of lapis laquli, as well as the major source of the gems best color?
Afghanistan
296
Which 3 materials are commonly used as lapis lazuli imitations?
Glass, Plastic, Ceramic
297
Which 3 things is turquoise judged uppon?
Color, Texture, Matrix
298
What effect does iron have on turquoise?
Greenish blue color
299
What effect does copper have on turquoise?
Desirable pure blue color
300
True or false – turquoise in matrix and with spider web commands the highest prices
FALSE
301
What is the most common cut of turquoise?
Cabochons, may also be cut into beads or flats for inlay
302
Turquoise that's porous and coarse is commonly treated to improve which 2 things?
Color and texture
303
Who is the largest producer of turquoise?
Southwestern US
304
Who is the major source of top color turquoise?
China's Hubei Province
305
Who has the largest, most consistent turquoise market?
Southwestern US
306
What is the most common turquoise imitation material?
Plastic
307
Feldspar, spodumene, and diopside are hard or soft gems?
Soft
308
Feldspar, spodumene, and diopside have cleavage in how many directions?
Two
309
True or false – feldspars are among the rarest minerals on earth?
False, Feldspars are the most widespread minerals on earth
310
The phenomenal moonstone fariety includes what?
All adularescent feldspars
311
What causes moonstones adularescence?
Scattering of light by stacked, alternating mineral layers
312
Describe moonstone's finest color
Colorless, semitransparent to nearly transparent appearance and vivid blue adularescence
313
What is the most common cutting style for moonstone?
Cabochon
314
Is moonstone readily available in commercial quality? Fine quality?
Readily available in modestly priced calibrated sizes, much more rare and expensive in fine quality
315
What causes labradorite's phenomenal colors?
Interference of light reflecting off the gem's layered structure
316
Which kind of phenomenal labradorite is most prized?
Spectrolite, brilliant spectral hues
317
What gives sunstone a reddish or golden sheen?
Small inclusions, large inclusions create glittering reflections
318
Sunstone from where isn't treated and that fact is used as a selling point?
Oregon, US
319
Kunzite is most commonly what color?
Pink
320
What is kunzite's most valuable colors?
Intense pink and intense violetish purple
321
How stable is spodumene treated with irradiation then heat to get kunzite's valuable pinkish color?
Can fade under heat or bright light
322
Why is chrome diopside an effective emerald alternative?
High clarity and lack of treatment
323
When can tree resin be called amber?
Harden over time and be at least 1 million years old
324
Which two places are amber's primary sources?
Baltic Sea region and the Dominican Republic
325
What are the two basic types of gem coral?
Calcareous coral and conchiolin coral
326
What do dealers call the most valuable red coral?
Oxblood
327
Why are many coral color terms Italian?
Because italy is the most imprtant coral marketing center
328
Jet was popular as mourning jewelry in what era?
Late Victorian
