Gemstone	Treatment	Frequency	Remarks
	Diamond	Laser Drilled	Sometimes	Diamonds are laser drilled to bleach out  dark inclusions.
	Diamond	Clarity Enhanced	Sometimes	Inclusions breaking the surface of the gemstone can be masked by placing a glass like substance in the crack.  The substance tends to mask the location of the crack.
	Emerald	Oiling	Usually	When observing an emerald it is best to assume the gemstone has been oiled.
	Emerald	Epoxy like filler	Often	Many emeralds are treated with an epoxy like filler.  The filler flows into the cracks on the surface of the gemstone.  The filler tends to mask or hide the location of these cracks.
	Sapphire	heated	Usually	Most sapphires are heated to improve the color of the gemstone or the uniform distribution of color within the gemstone.
	Ruby	Heated	Usually	Heated to improve color
	Ruby	Dyed	Rarely	Dyed with colored oil to improve appearance
	Ruby	Heated to seal fractures	Often	Rubies are heated in a controlled environment in a borax solution.  The borax can heal fractures in the surface of the stone.   Occasionally the borax residue can be seen under 10 power magnification.
	Ruby	Clarity Enhanced	Occasionally	Rubies are occasionally Intentionally treated with a substance that  fills surface cavities and fractures with a foreign material. This filler can have glass like properties
	Amethyst	Heated	Occasionally	Amethyst is sometimes heated to lighten the color or remove a brownish component
	Citrine	Heated	Usually	Amethyst is often heated to lighten the color to a yellow or yellow brown
	Tanzanite	Heated	Always	Zoisite (Tanzanite) is typically a yellowish brown color when mined.  The gemstone is heated to produce the bluish purple to purplish blue color the public prizes
	Blue Topaz	Irradiated	Always	The gemstone is bombarded by neutrons to produce the blue color.
	Pearls	Bleached	Usually	Cultured Pearls are usually bleached to improve color.
	Pearls	Dyed	Occasionally	Black or gray pearls are typically dyed to these shades.   Rose or blue tints are sometimes the product of dying.  Freshwater pearls in a variety of colors are usually dyed.
	Pearls	Irradiated	Occasionally	Pearls are occasionally irradiated to produce black or gray colors.
	More to follow at a later date..			If you have a particular question about a gemstone