Information Source: Gem Reference Guide. Gemological Institute of America, 1995.

Gemstone/
Origin
Description Treatment Effects Care Cleaning
Amethyst
(quartz) / Natural
Purple through bluish purple Heat treatment Lightens the color of very dark amethyst; removes smoky component of color None Ultrasonic: Usually safe
Steamer: Risky
Warm Soapy Water: Safe
Aquamarine
(beryl) / Natural
Greenish blue through blue-green Heat treatment Produces blue from green, iron-colored material None Ultrasonic: Usually safe, unless stone contains feathers or liquid inclusions
Steamer: Usually safe, unless stone contains feathers or liquid inclusions
Warm Soapy Water: Safe
Black Cultured Pearl
/ Organic
Contains body colors of black, dark gray, or dark tones of blue, purple, green, or bronze Irradiation To produce "black" pearls (also gray or blue gray) from bleached pearls Wipe with very soft cloth after each wearing Ultrasonic: Never
Steamer: Never
Warm Soapy Water: Safe for more thorough cleaning (if strung, be sure string is completely dry before washing)
Blue Quartz / Lab Created Meduim sky blue        
Blue Topaz / Natural Very slightly greenish blue to greenish blue Irradiation Produces a blue color in irradiated stones Avoid heat and prolonged exposure to strong light; if radioactive (rare), avoid handling and wear Ultrasonic: Never
Steamer: Never
Warm Soapy Water: Safe
Citrine
(quartz) / Natural
Yellow through orange Heat treatment Produces citrine from amethyst Avoid steam Ultrasonic: Usually safe
Steamer: Risky
Warm Soapy Water: Safe
Created Ruby (synthetic corundum) / Lab Created Very strong orangy red Quench cracking (heating and then plunging it into cold water) Produces cracks which imitate natural breaks and fingerprint inclusions Avoid rough wear Ultrasonic: Usually safe, but never for oiled stones
Steamer: Usually safe, but never for oiled stones
Warm Soapy Water: Safe, but avoid strong detergents and vigorous scrubbing on oiled stones
Cubic Zirconia
(synthetic) / Lab Created
Colorless None   None Ultrasonic: Safe
Steamer: Safe
Warm Soapy Water: Safe
Cultured Pearl
/ Organic
Translucent to opaque · Bleaching
· Dyeing
· Bleach dark spots of conchiolin that show through the nacre
· To alter the body color or hide colored blemishes
Wipe with very soft cloth after each wearing Ultrasonic: Never
Steamer: Never
Warm Soapy Water: Safe for more thorough cleaning (if strung, be sure string is completely dry before washing)
Emerald
(beryl) / Natural
Very strongly bluish green through green Oiling (oil may contain green dye) Hides flaws, improves transparency, may deepen color Keep away from strong solvents, heat, and ultrasonic cleaners Ultrasonic: Never
Steamer: Never
Warm Soapy Water: Generally safe, but avoid strong detergents and vigorous scrubbing on oiled stones
Garnet
(pyrope) / Natural
Red through slightly purplish red None known   None Ultrasonic: Usually safe
Steamer: Risky
Warm Soapy Water: Safe
Iolite / Natural Violet-blue through slightly violet-blue None known   None Ultrasonic: Risky
Steamer: Risky
Warm Soapy Water: Safe
Mother of Pearl
(shell) / Organic
Translucent to opaque Dyeing To produce a variety of colors Avoid solvents and prolonged exposure to strong light Ultrasonic: Risky
Steamer: Risky
Warm Soapy Water: Safe
Mount St. Helens / Lab Created Deep, clean bluish green        
Mystic Fire Topaz / Natural Greenish Coated Changes clear topaz to color Normal Ultrasonic: Unsafe
Steamer: Unsafe
Warm Soapy Water: Safe
Onyx
(chalcedony) / Natural
Solid black color Dyeing Chalcedony is dyed to practically all colors for various uses; the bands in agate and onyx accept dye differently so that a green dye, for example, may impart color to some layers and leave others white None Ultrasonic: Usually safe
Steamer: Usually safe
Warm Soapy Water: Safe
Peridot / Natural Yellowish green through greenish yellow No commercial treatments known   None Ultrasonic: Risky
Steamer: Never
Warm Soapy Water: Safe
Pink Sapphire
(corundum) / Natural
Red through purple Coating with a thin film Creates, deepens, or changes the color of a sapphire Avoid abrasions Ultrasonic: Usually safe
Steamer: Usually safe
Warm Soapy Water: Safe
Pink Tourmaline / Natural Red-orange through reddish purple Irradiation Produces a deep pink to red to deep purple from very light pink, green, blue, or colorless None Ultrasonic: Risky
Steamer: Risky
Warm Soapy Water: Safe
Rhodolite Garnet / Natural Slightly purplish red through reddish purple None known   None Ultrasonic: Usually safe
Steamer: Never
Warm Soapy Water: Safe
Ruby
(corundum) / Natural
Orange-red through strongly purplish red Heat treatment Removes purple or brownish color component None Ultrasonic: Usually safe, but never for oiled stones
Steamer: Usually safe, but never for oiled stones
Warm Soapy Water: Safe, but avoid strong detergents and vigorous scrubbing on oiled stones
Sapphire
(corundum) / Natural
Violet-blue through greenish blue Heat treatment Produces blue sapphire from milky "gueda" sapphire None Ultrasonic: Usually safe
Steamer: Usually safe
Warm Soapy Water: Safe
Tanvorite / Lab Created Deep, clean bluish/purple        
Tanzanite
(zoisite) / Natural
Bluish purple and violet through blue Heat treatment Produces tanzanite colors in certain crystals with initially brownish colors None Ultrasonic: Never
Steamer: Never
Warm Soapy Water: Safe
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