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. This Guide covers enhancement methods known or believed to help these gems reach their full potential for beauty or improve their durability.
| Gemstone | Hardness | Method | Code | Frequency | Stability | Care and 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 - see Chalcedony |
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| Alexandrite | 8.5 | none | N | n/a | n/a | normal care |
| Almandite - see Garnet |
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| 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 |
| Amblygonite | 6 | none | N | n/a | n/a | *Research in Progress |
| Amethyst - see Quartz |
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| 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 |
| 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 |
| Azurmalachite | 3.5-4 | filled with epoxy or resin | I | r | f-g | soft/avoid heat, harsh chemicals and ultrasonic |
| Benitoite | 6.5 | none | N | n/a | n/a | avoid heat, harsh chemicals and ultrasonic |
| 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 |
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| Cat's eye - see Chrysoberyl |
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| 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 |
| 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 |
| 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 | |||||
| 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 |
| Diaspore | 6.5-7 | none | N | n/a | n/a | normal |
| Diopside | 5-6 | none | N | n/a | n/a | moderately soft, avoid sudden temperature changes, and harsh chemicals |
| Dravite - see Tourmaline |
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| 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 |
| 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 |
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| 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 |
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| Indicolite - see Blue Tourmaline |
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| Iolite | 7-7.5 | none | N | n/a | n/a | normal |
| 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 |
| 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 |
| 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 |
| Kyanite | 4-7 | none | N | n/a | n/a | very soft in certain directions |
| Kunzite - see Spodumene |
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| 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 |
| 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 |
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| Morganite - see Beryl |
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| Moss Agate - see Chalcedony |
6.5-7 | |||||
| Nephrite - see Jade |
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| Oligoclase - see Feldspar |
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| 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 |
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| Padparadscha - see Sapphire |
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| 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 |
| 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 |
| Petalite | 6-6.5 | *Research in Progress | * | * | * | *Research in Progress |
| Phenakite | 7.5-8 | *Research in Progress | * | * | * | normal care |
| Petrified Wood | 6.5-7 | none | N | n/a | n/a | normal care |
| 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 | |||||
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| Shell | 4 | dyed | D | c | f-g | avoid harsh chemicals |
| Sinhalite | 6.5-7 | *Research in Progress | * | * | * | *Research in Progress |
| Sodalite | 5.5-6 | dyed | D | r | f | color may fade |
| 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 |
| Spinel (all colors) |
8 | none | N | n/a | n/a | normal care |
| 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 |
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| Tanzanite - see Zoisite |
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| 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 |
| Taaffeite | 8-8.5 | none | N | n/a | n/a | normal care |
| 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 |
| Unakite | 6-7 | none | N | n/a | n/a | avoid harsh chemicals |
| Variscite | 4-5 | none | N | n/a | n/a | may fade in strong light |
| Verdelite - see Green Tourmaline |
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| 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 |
| Zoisite | ||||||
| Tanzanite | 6.5-7 | heated to produce violet/blue color | E/H | u | e | special care due to hardness |