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Gemstone Enhancement & Treatment

The fashioning of gemstones is a skillful blend of art and science. Art is used to shape, facet and polish. Science is used to attain the finest color and appearance. As part of its commitment to consumer education, Certified Gemological Information presents this comprehensive directory of gems, including well known as well as rare and exotic varieties. It also covers enhancement methods known or believed to help these gems reach their full potential for beauty or improve their durability.

Gemstone Hard Method Cd Frequ Stab Care/Handling
Abalone
Shell 3-4 none N n/a n/a avoid heat / harsh chemicals / perfumes / hairsprays
Pearl 2.5-4 none N n/a n/a avoid heat / harsh chemicals / perfumes / hairsprays
Agate – seeChalcedony
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Alexandrite 8.5 none N n/a n/a normal care
Almandite – see Garnet
Amazonite – see Feldspar
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Amber
Amber 2-2.5 none N r n/a very soft / avoid harsh chemicals and ultrasonic
Amber 2-2.5 heated to improve appearance or deepen color E/H u g-vg very soft / avoid harsh chemicals and ultrasonic
Amber 2-2.5 dyed or surface treated to add color D r v avoid repolishing, harsh chemicals and ultrasonic
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Amblygonite 6 none N n/a n/a *Research in Progress
Amethyst -see Quartz
Ametrine -see Quartz
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Ammonite / Ammolite 4 impregnated with colorless hardened substances to increase stability I u f-g avoid heat, harsh chemicals and ultrasonic
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Andalusite 7-7.5 none N n/a n/a normal care
Andradite – see Garnet
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Apatite
Apatite 5 none N r n/a moderately soft, avoid heat, harsh chemicals and ultrasonic
Apatite 5 heated to improve appearance or deepen color H u g moderately soft, avoid heat, harsh chemicals and ultrasonic
Aquamarine – see Beryl
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Aragonite 3.5-4 none N n/a n/a soft/avoid heat, harsh chemicals and ultrasonic; generally unsuitable for jewelry
Aventurine – see Quartz
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Azurite 3.5-4 coated with colorless wax C o f-g soft/avoid heat, harsh chemicals and ultrasonic
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Azurmalachite 3.5-4 filled with epoxy or resin I r f-g soft/avoid heat, harsh chemicals and ultrasonic
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Benitoite 6.5 none N n/a n/a avoid heat, harsh chemicals and ultrasonic
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Beryl
Aquamarine 7.5-8 none N vr n/a normal care
Aquamarine 7.5-8 heated to improve color E/H u et normal care
Blue (Maxixe) 7.5-8 irradiated blue from pale pink or colorless R a p extra special – avoid light and heat/color fades
Colorless (Goshenite) 7.5-8 none N n/a n/a normal care
Emerald 7.5-8 none N er n/a avoid sudden temperature change, ultrasonic and chemicals
Emerald 7.5-8 dyed with colored agents D o v avoid sudden temperature changes, chemicals and ultrasonic
Emerald 7.5-8 penetration of colorless oils, wax and resins into fissures to improve appearance E/O u f-vg avoid sudden temperature changes, chemicals and ultrasonic
Pink (Morganite) 7.5-8 heated to remove yellow E/H c e normal care
Red (Bixbite) 7.5-8 none N r n/a avoid high temperatures, steam cleaning, chemicals, ultrasonic
Red (Bixbite) 7.5-8 colorless oil and resins to improve appearance E/O c f-vg avoid high temperatures, steam cleaning, chemicals, ultrasonic
Yellow 7.5-8 irradiated to produce color R u v normal care, but some stones may fade in light or heat
Green – Yellow 7.5-8 none N n/a n/a normal care
Carnelian -see Chalcedony
Cat’s eye -see Chrysoberyl
Bone – see Ivory
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Chalcedony
Agate 6.5-7 dyed D u g-e normal care
Black Onyx 6.5-7 dyed D a g-e normal care
Banded Agate 6.5-7 dyed D u e normal care
Bloodstone 6.5-7 *Research in Progress * * * normal care – *Research in Progress
Blue Chalcedony 6.5-7 dyed D c f-g may fade in light or heat
Carnelian 6.5-7 heated to produce color E/H u e normal
Carnelian 6.5-7 dyed to produce color D o g-e certain stones may fade in light or heat
Chrysoprase 6.5-7 none N n/a n/a normal care
Dendritic Agate 6.5-7 none N n/a n/a normal care
Fire Agate 6.5-7 none N n/a n/a normal care
Green Chalcedony 6.5-7 dyed to produce color D u f-g may fade in light or heat
Moss Agate 6.5-7 none N n/a n/a normal care
Jasper 6.5-7 sometimes dyed to imitate other stones D o e normal care
Sard 6.5-7 heated to produce color E/H u e normal
Sard 6.5-7 dyed to produce color D o g-e certain stones may fade in light or heat
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Chrome Diopside 5-6 none N n/a n/a moderately soft, avoid sudden temperature changes, harsh chemicals
Chrome Tourmaline – see Tourmaline
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Chrysoberyl
Cat’s Eye 8.5 none N n/a n/a normal
Cat’s Eye 8.5 irradiated to change color R o e normal
Brown, Yellow, Green 8.5 none N n/a n/a normal
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Coral
Black 3-4 none N n/a n/a special – avoid chemicals, cosmetics and ultrasonic
White 3-4 bleached E/B c g special – avoid chemicals, cosmetics and ultrasonic
Pink 3-4 impregnated with colorless wax E/W c g special – avoid chemicals and ultrasonic
Orange 3-4 stabilized with plastic to improve color and durability I c g special – avoid chemicals and ultrasonic
Gold 3-4 bleached from black coral B c v-g avoid chemicals and ultrasonic
Red 3-4 dyed D u v special to extra special depending on type of dye – avoid chemicals, cosmetics and ultrasonic
Corundum – see Sapphire / Ruby o
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Danburite
White 7-7.5 none N n/a n/a normal care
Brown 7-7.5 irradiated R c g *Research in Progress
Demantoid – see Garnet
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Diamond
Diamond 10 none N n/a n/a normal
Diamond 10 laser drilled to improve appearance L o v-g normal
Colorless to Faint Yellow 10 coated to disguise off color C r p-vg color may be affected by polishing, recutting, ultrasonic, alcohol and harsh chemicals
Colorless to Faint Yellow 10 fracture filled to improve clarity F o v-g avoid extreme heat and recutting
Colorless to Faint Yellow 10 heat pressure treated HP r u normal
Colored 10 use of heat to alter color H r u normal
Colored 10 laser drilled to improve appearance L o v-g normal
Colored 10 irradiated and/or heated to produce a variety of colors R o e-vg normal
Colored 10 fracture filled to improve clarity F r v-g avoid extreme heat and recutting
Green 10 Irradiated and/or heated to produce green R o e-vg special care – avoid heating, color may change
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Diaspore 6.5-7 none N n/a n/a normal
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Diopside 5-6 none N n/a n/a moderately soft, avoid sudden temperature changes, and harsh chemicals
Dravite – see Tourmaline
Emerald – see Beryl
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Feldspar
Amazonite 6-6.5 impregnated with colorless wax, paraffin or oil E/W u f-g avoid extreme heat, harsh chemicals and ultrasonic
Amazonite 6-6.5 impregnated with hardened resins I u v-g avoid chemicals and ultrasonic
Labradorite / Spectrolite 6-6.5 none N n/a n/a *Research in Progress
Moonstone 6-6.5 none N n/a n/a normal
Orthoclase 6-6.5 none N n/a n/a *Research in Progress
Plagioclase 6-6.5 none N n/a n/a *Research in Progress
Sunstone 6-6.5 none N n/a n/a *Research in Progress
Fire Agate – see Chalcedony
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Fluorite
Colorless/ Colored 4 none N n/a n/a soft, avoid harsh chemicals
Blue, Green, Purple 4 irradiated to produce color R u u soft, avoid harsh chemicals
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Garnet
Almandite 7-7.5 none N n/a n/a normal – avoid sudden temperature change
Demantoid 6.5-7 none N n/a n/a normal
Grossular 7-7.5 none N n/a n/a normal
Hessonite 7-7.5 none N n/a n/a normal
Pyrope 7-7.5 none N n/a n/a normal
Rhodolite 7-7.5 none N n/a n/a normal
Spessartite (Mandarin) 7-7.5 none N n/a n/a normal
Topazolite 6.5-7 none N n/a n/a normal
Tsavorite 7-7.5 none N n/a n/a normal
Uvarovite 7-7.5 none N n/a n/a normal
Goshenite – see Beryl 7.5-8
Green Tourmaline – see Tourmaline
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Hematite 5.5-6.5 none N n/a n/a normal
Hessonite – see Garnet
Hiddenite – see Spodumene
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Howlite
White 3.3-5 none N na n/a *Research in Progress
Blue 3-3.5 dyed to imitate turquoise D c g Very soft, avoid harsh chemicals, ultrasonic, and steaming
Hyacinth – see Zircon
Indicolite – see Blue Tourmaline
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Iolite 7-7.5 none N n/a n/a normal
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Ivory
Ivory / Bone 2-3 bleached to whiten and remove discoloration E/B c g very soft, avoid chemicals and ultrasonic, may discolor with time
Ivory / Bone 2-3 dyed for artistic purposes D o g very soft, avoid chemicals and ultrasonic, may discolor with time
Ivory / Bone 2-3 impregnated with colorless paraffin wax W o g very soft, avoid chemicals and ultrasonic, may discolor with time
Ivory / Mammoth 2-3 impregnated with colorless hardened substances to increase stability I c g normal
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Jade
Jadeite 6.5-7 coated with colorless wax E/W c f avoid ultrasonic and harsh chemicals
Jadeite 6.5-7 bleached and wax impregnated B/W r p avoid heat, harsh chemicals and ultrasonic
Jadeite(Green, White, Purple) 6.5-7 bleached and polymer impregnated B/I c g-vg avoid heat, harsh chemicals and ultrasonic
Jadeite (Green, White, Purple) 6.5-7 dyed to imitate natural colors D o v avoid strong light, chemicals and ultrasonic
Nephrite 6-6.5 dyed D r u avoid strong light, harsh chemicals and ultrasonic, may discolor with time
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Kornerupine
Kornerupine 6.5-7 none N n/a n/a *Research in Progress
Cat’s Eye Kornerupine 6.5-7 none N n/a n/a *Research in Progress
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Kyanite 4-7 none N n/a n/a very soft in certain directions
Kunzite – see Spodumene
Labradorite – see Feldspar
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Lapis Lazuli
Lapis Lazuli 5-6 coated with wax or oil E/W c f avoid chemicals and ultrasonic
Lapis Lazuli 5-6 dyed to produce color or uniformity in color D c v avoid chemicals and ultrasonic
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Malachite
Malachite 3.5-4 coated with colorless wax W o f soft, avoid chemicals and ultrasonic
Malachite 3.5-4 impregnated with plastic and/or other hardened agents I r g soft, avoid chemicals and ultrasonic
Mandarin Garnet – see Spessartite
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Marcasite 6-6.5 none N n/a n/a normal
Maxixe – see Beryl
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Moldavite 5.5 none N n/a n/a normal
Moonstone -see Feldspar
Morganite – see Beryl
Moss Agate – see Chalcedony 6.5-7
Nephrite – see Jade
Oligoclase – see Feldspar
Olivine – see Peridot
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Opal
White, Black, Semi-Black 5.5-6.5 natural N n/a n/a avoid excessive heat / ultrasonic
White, Black, Semi-Black 5.5-6.5 impregnated with colorless oil, wax and resins O r f avoid excessive heat, solvents and ultrasonic
White, Black, Semi-Black 5.5-6.5 impregnated with colorless plastic to improve durability and color I r g avoid excessive heat and solvents
Boulder 5.5-6.5 infusion of unhardened colorless substances to improve appearance O o f avoid heat, chemicals, ultrasonic and repolishing
Cat’s Eye Opal 5.5-6.5 impregnated with colorless plastic to improve durability and color I u g avoid heat, chemicals, and ultrasonic
Fire Opal 5.5-6.5 none N n/a n/a avoid heat
Hydrophane 5.5-6.5 impregnated with colorless oil, wax and resins O c f avoid heat and solvents
Hydrophane 5.5-6.5 impregnated with colorless plastic to improve durability and color I c g avoid heat and solvents
Hydrophane 5.5-6.5 dyed D c g avoid heat and solvents
Matrix 5.5-6.5 sugar solution infilling in acid bath to darken background D c g avoid heat, solvents and repolishing
Orthoclase – see Feldspar
Padparadscha – see Sapphire
Paraiba Tourmaline – see Tourmaline
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Pearl
Natural 2.5-4.5 bleached to improve color and appearance B/E u vg special care – avoid cosmetics and household chemicals
Natural 2.5-4.5 dyed with or without chemical treatment combined with heat to produce gray to black D r g-vg special care – avoid cosmetics and household chemicals and ultrasonic
Cultured 2.5-4.5 bleached to improve color and uniformity of white color only B/E u e special care – same as above
Cultured 2.5-4.5 dyed to give rose, blue or golden overtones D u g special care – same as above
Cultured 2.5-4.5 dyed blue, black and other colors includes use of colored nuclei D o v special care – same as above
Cultured 2.5-4.5 dyed all colors (freshwater) D u vg special care – same as above
Cultured 2.5-4.5 irradiated to produce blue, gray, black and bronze colors R o vg special care – same as above
Cultured 2.5-4.5 chemical treatment combined with heat to produce gray to black D c g-vg special care – same as above
Mabe 2.5-4.5 color coated, dyed, bleached, filled with a hardened substance and a MOP back. Sometimes coating can be plastic or polymer to protect the thin nacre B/D/I (ASBL) a f-vg extra special care – avoid household chemicals, cosmetics, abrasives, and sudden shocks
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Peridot
Peridot 6.5-7 none N n/a n/a normal care
Peridot 6.5-7 impregnated with colorless oil, wax and resins E/O r f-g avoid sudden temperature changes, harsh chemicals and ultrasonic
Peridot 6.5-7 surface fracture filling with a colorless hardened substance F r g avoid sudden temperature changes, harsh chemicals and ultrasonic
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Petalite 6-6.5 *Research in Progress * * * *Research in Progress
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Phenakite 7.5-8 *Research in Progress * * * normal care
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Petrified Wood 6.5-7 none N n/a n/a normal care
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Pietersite 7 none N n/a n/a normal care
Pink Tourmaline – see Tourmaline
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Pyrite 6-6.5 none N n/a n/a avoid harsh chemicals and excessive heat
Pyrope – see Garnet 7-7.5
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Quartz
Amethyst 7 none N n/a n/a may fade with long exposure to sunlight
Amethyst 7 heated to improve color H r e avoid exposure to high heat
Ametrine 7 none N n/a n/a normal care
Aventurine 7 none N n/a n/a normal care
Black 7 irradiated to alter color R u g-e normal care
Citrine 7 heated to improve color E/H u e normal care
Ginger 7 irradiated to alter color R a e normal care
Lilac 7 heated to improve color H o e normal care
Oro Verde 7 irradiated and heated to produce color R a e normal care
Smoky 7 irradiated to alter color R u g normal care
Rock (Colorless) 7 none N n/a n/a normal care
Rose 7 natural N n/a n/a normal care
Tourmalinated 7 none N n/a n/a normal care
Rutilated 7 none N n/a n/a normal care
Tiger’s Eye 7 bleached, dyed or heated B/D/H o g-vg avoid harsh chemicals, ultrasonic and steaming
Violet 7 heated to improve color H o g-e normal care
Watermelon 7 heated to improve color H o g-e normal care
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Rhodochrosite 3.5-4 none N n/a n/a very soft
Rhodolite – see Garnet
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Rhodonite 5.5-6 dyed to make color uniform D o p special care – avoid chemicals and ultrasonic
Rubellite-see Tourmaline (Red)
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Ruby
Ruby 9 natural N n/a n/a normal care
Ruby 9 heated to improve color and clarity E/H u g-e normal care
Ruby 9 irradiated to change color R r u normal care
Ruby 9 intentional filling of surface cavities and fractures F/Fh c f-vg avoid caustic acids, extreme pressure, heat and ultrasonic
Ruby 9 surface or lattice (bulk) diffusion penetrating most/all of the stone U o g special care – avoid repolishing/recutting
Ruby 9 dyed with colored oil to improve appearance D r p special care – avoid harsh chemicals and ultrasonic
Star Ruby 9 surface diffusion of color or asterism U o g special care – avoid repolishing/recutting
Star Ruby 9 heated to improve color/asterism E/H c g-e normal care
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Sapphire
Sapphire 9 natural N n/a n/a normal care
Sapphire 9 heated to improve color/clarity E/H u e normal care
Sapphire 9 surface or lattice (bulk) diffusion penetrating most/all of the stone U o g special care – avoid repolishing/recutting
Sapphire 9 irradiation to produce temporary yellow or orange color R o vp extra special – fades quickly in light or heat
Star Sapphire 9 surface diffusion of color or asterism U o g special care – avoid repolishing/recutting
White (Colorless) 9 heated to improve color/clarity E/H u g-e normal care
Black Star 9 heated E/H u vg normal care
Fancy Colors(Green, Orange, Purple, Pink, Padparadscha, Yellow) 9 surface or lattice (bulk) diffusion penetrating most/all of the stone E/H c f-g special care – avoid repolishing/recutting
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Scapolite
Yellow 5.5-6 none N n/a n/a avoid ultrasonic cleaners and exposure to strong sunlight
Violet 5.5-6 *Research in Progress * * * *Research in Progress
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Serpentine
Serpentine 2.5-5.5 dyed D c f-g color may fade
Serpentine 2.5-5.5 impregnated with colorless wax E/W c g-vg avoid ultrasonic, chemicals and solvents
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Shell 4 dyed D c f-g avoid harsh chemicals
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Sinhalite 6.5-7 *Research in Progress * * * *Research in Progress
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Sodalite 5.5-6 dyed D r f color may fade
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Sphalerite 3.5-4 none N n/a n/a very soft stone, generally not suited for jewelry use
Spessartite – see Garnet
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Sphene 5-5.5 none N n/a n/a normal care, best used in earrings & pendants due to softness
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Spinel (all colors) 8 none N n/a n/a normal care
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Spodumene
Kunzite 6.5-7 irradiated & heated R c f avoid strong light/ultrasonic
Kunzite 6.5-7 heated to improve color E/H c f color may fade in strong light/sunlight, avoid ulltrasonic
Hiddenite (Green) 6.5-7 none N n/a n/a color fades in light or heat
Hiddenite (Green) 6.5-7 irradiated to produce green color R r p extra special care – color fades in light or heat
Yellow 6.5-7 irradiated to produce yellow color R r p extra special care – color fades in light or heat
Sugulite 6-6.5 none N n/a n/a normal care
Sunstone – see Feldspar
Tanzanite – see Zoisite
Tiger’s Eye – see Quartz
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Topaz
Blue 8 irradiated and/or heated to produce blue color R u e normal care
Brown 8 none N n/a n/a may fade with exposure to sunlight
Brown 8 irradiated R o p will fade
Green 8 irradiated to improve the color R o p extra special care – color fades in exposure to sunlight
Green 8 diffusion of color at or near the surface U u g special care – avoid repolishing or recutting
Mystic, Ocean, Glacier, Patriot, Canary, Champagne, Orchid, Dawn, Teal, Kiwi (others) 8 enhanced with various coatings to produce a variety of colors (chemical vapor deposition) C a f avoid harsh chemicals, heat, ultrasonic cleaners and repolishing/recutting
Pink/Red 8 heated chromium-bearing pinkish-brown to orange stones E/H u e normal care
Yellow / Orange 8 irradiated to intensify color R o v special care – avoid heat and strong light
White 8 none N n/a n/a normal care
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Taaffeite 8-8.5 none N n/a n/a normal care
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Tourmaline
Cat’s Eye 7-7.5 none N n/a n/a normal care
Chrome 7-7.5 none N n/a n/a normal care
Green, Blue 7-7.5 none N n/a n/a normal care
Green, Blue 7-7.5 heated to improve color E/H c e normal care
Green, Blue 7-7.5 the penetration of colorless oils / unhardened resins O o f-g avoid steaming, chemicals, ultrasonic, and temperature changes
Paraiba 7-7.5 heated to improve color E/H c g-vg normal care
Pink, Red, Purple 7-7.5 heated to improve color E/H o e normal care
Pink, Red, Purple 7-7.5 irradiated to intensify color R c g normal care
Pink, Red, Purple 7-7.5 penetration of colorless oils or unhardened resins into fissures to improve appearance O o f-g special care – avoid temperature changes, steaming, chemicals and ultrasonic
Pink, Red, Purple 7-7.5 penetration of coloring agents into voids to improve appearance D o p-f special care – avoid temperature changes, steaming, chemicals and ultrasonic
Yellow / Orange 7-7.5 heated to improve color E/H r e normal care
Yellow / Orange 7-7.5 irradiated to improve color R r vg normal care
Tsavorite – see Garnet
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Turquoise
Turquoise 5-6 impregnated with plastic to create or improve color and increase durability I c g special care – avoid hot water, household chemicals, and ultrasonic
Turquoise 5-6 impregnated with colorless oil or wax to enhance or create color W c p-f special care – avoid hot water, household chemicals, and ultrasonic
Turquoise 5-6 dyed to improve color D r p special care – avoid hot water, harsh household chemicals, and ultrasonic
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Unakite 6-7 none N n/a n/a avoid harsh chemicals
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Variscite 4-5 none N n/a n/a may fade in strong light
Verdelite – see Green Tourmaline
Yellow Beryl – see Beryl
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Zircon
Blue, Colorless 6.5-7 brownish crystals are heated to improve these colors E/H a p-f special care – avoid harsh abrasives and strong light
Green / Brown 6.5-7 none N n/a n/a special care – avoid harsh abrasives
Red 6.5-7 heated to change brownish crystals to red E/H c p-f special care – avoid harsh abrasives
Yellow 6.5-7 heated to improve color E/H r g-f special care – avoid harsh abrasives
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Zoisite
Tanzanite 6.5-7 heated to produce violet/blue color E/H u e special care due to hardness

 

*Research in Progress

Complete information regarding the possible enhancement/special care on this gem is currently being researched due to the rarity of this stone in the jewelry trade. Our sources include, but are not limited to, university mineralogical, gemological, geology departments, as well as gem laboratories, the Internet, and individual experts in the trade. Updates will be made as more information becomes available.

Gemstone Enhancement Codes (based on AGTA guidelines)

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B=Bleaching

The use of heat, light and/or chemicals or other agents to lighten or remove a gemstone’s color. This is often accompanied by subsequent dying and/or impregnation. Example: bleached cultured pearl; bleached/impregnated jadeite (‘B-jade)

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C=Coating

The use of such surface enhancements as lacquering, enameling, inking, foiling, or sputtering of films to improve appearance, provide color or add other special effects. Example: coated diamond, coated topaz

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D=Dyeing (Staining)

The introduction of coloring matter into a gemstone to give it new color, intensify existing color or improve color uniformity. Example: dyed green jadeite

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E=Normally Enhanced

The “E” symbol is used for gemstones that are routinely enhanced. Since many enhancements are difficult or impractical to prove definitively, unless otherwise indicated, our approach is to assume that such enhancements have been applied to that particular gemstone. This assumption is made to protect both buyer and seller. If a more specific method of enhancement is known, then the specific enhancement code will be used.

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F=Filling

The filling of surface-breaking cavities or fissures with colorless glass, plastic, or some similar substance. This process will improve durability, appearance and/or weight. Example: ruby

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Fh=Flux healing

During heat enhancement, fluxes (or heat alone) may be used to heal fractures/fissures which were formerly open. The process dissolves the walls of the fractures and redeposits the molten gem material, healing the fractures closed. Example: ruby (particularly that from Mong Hsu, Burma)

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H=Heating

The use of heat to alter color, clarity, and/or phenomena. Example: Ruby, sapphire, tanzanite, aquamarine, demantoid garnet

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HP=Heating & Pressure

The use of heat and pressure combined to affect desired alterations of color and/or clarity.

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I=Impregnation

The impregnation of a porous gemstone with a colorless agent (usually plastic) to give it durability and improve appearance. Example: Stabilized turquoise.

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L=Lasering

The use of a laser and chemicals to reach and alter inclusions. Example: diamond

N=Not Enhanced

The “N” symbol is used on our invoices to indicate one of two situations. First, there are certain gemstones that are not currently known to be enhanced (alexandrite, some garnets, etc.) Second the “N” symbol may also be used for a gem where it can be proved via gemological or other means that a gem has not been subjected to any enhancement. When you see the “N” symbol on our invoice, we guarantee that the gem in question is unenhanced.

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O=Oiling/Resin Infusion

The filling of surface-breaking fissures with a colorless oil, wax, resin or other colorless substances, except glass or plastic, to improve the gemstone’s appearance. Example: emerald

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R=Irradiation

The use of neutrons, gamma, ultraviolet and/or electron bombardment to alter a gemstone’s color. The irradiation may be followed by a heating process. Example: Blue topaz, colored diamonds

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U=Lattice (‘bulk’ or ‘surface’) Diffusion

Outside-in diffusion of coloring chemicals via high-temperature heat treatment to produce color and/or asterism. Example: lattice diffusion-treated sapphire

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W=Waxing/Oiling

The impregnation of a colorless wax; paraffin and/or oil in porous gemstones to improve appearance. Example: jadeite

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Stability Abbreviation Chart

e Excellent
vg-e Very good to excellent
g-e Good to excellent
g-vg Good to very good
vg Very Good
g Good
f-g Fair to good
f Fair
v Variable
u Unknown
p-vg Poor to Very Good
p-f Poor to Fair
p Poor
vp Very Poor
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Frequency Abbreviation Chart

r Rarely
u Usually
o Occasionally
vr Very Rare
a Always
er Extremely Rare
c Commonly
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