Alexandrite - None

Amazonite - Usually, the use of wax, paraffin or oil via impregnation; occasionally,

 use of plastic or hardening agents.

Amber - Occasionally, heated for sun spangles or color enhancement; rarely, dyed

 or surface treated.

Amethyst - Occasionally, heated to lighten color and to remove 'smoky'

 components.

Ametrine - None

Ammolite - Commonly treated with colorless hardening substances, for stability, via

 impregnation.

Andalusite - None

Aquamarine - Usually heated to remove yellow components (green) to leave the

 blue.

Beryl - Blue-Always irradiated blue from colorless; Pink-Commonly heated to

 remove the yellow component; Yellow/Green-None; Red-None; Yellow-Usually

 produced by irradiation.

Chalcedony - Agate-Usually dyed; (Black) Onyx-Always dyed; Banded-Usually

 dyed; Blue-Commonly dyed; Green-Usually dyed; Carnelian-Usually heated,

 occasionally dyed; Jasper-Occasionally dyed; Chrysoprase-None.

Chrysoberyl - Cat's Eye-Occasionally irradiated; Yellow or Brown or Green - None.

Citrine - Usually produced by heating various types of quartz.

Coral - Black-None; White-Commonly bleached; Pink-Commonly impregnated with

 colorless wax; Orange-Commonly stabilized with plastic; Gold- Usually bleached

 from black; Red-Occasionally dyed.

Diamond - Occasionally to commonly laser drilled; Rarely coated; Occasionally by

 filling surface cavities or fractures with a hardened substance; Occasionally

 irradiated and/or heated. Now a recent procedure (currently undetected) of taking a

 brown diamond and making it white.

Diopside - None.

Emerald - Usually the penetration of colorless oil, wax, unhardened resins into voids; Commonly

 the filling of surface cavities or fractures with a hardened colorless substance; Occasionally dyed

 with colored substance.

Garnet - None

Hematite - None

Iolite - None

Ivory & Bone - Commonly bleached; Occasionally dyed; Occasionally impregnated with colorless wax paraffin; Commonly impregnated with colorless hardened substances.

Jade - Commonly impregnated with colorless wax; Commonly bleached and polymer impregnated; Occasionally dyed.

Kunzite - Commonly heated and/or irradiated.

Lapis Lazuli - Commonly impregnated with colorless wax or oil; Commonly dyed.

Malachite - Occasionally coated with a colorless wax; Rarely impregnated with plastic and/or other hardened agents.

Moonstone - None

Opal - Rarely impregnated with colorless oil, wax and resins; Rarely impregnated with colorless plastic; Commonly sugar solution infilling in an acid bath; Occasionally infusion of unhardened essentially colorless substances into voids; Usually impregnated with colorless resins and hardeners.

Pearl - Usually bleached; Rarely dyed in natural pearls but usually dyed in cultured pearls; Occasionally irradiated; Commonly chemical treatment with heat.

Peridot - Rarely penetration of colorless oil, wax, unhardened resins into voids; Rarely filling of 

surface fractures with a colorless hardened substance.

Rhodochrosite - Rarely dyed.

Rhodonite - None.

Ruby - Usually heated; Rarely dyed; Commonly intentional filling of surface cavities and fractures

 with a foreign material, including glass; Commonly as a by-product of heat treatment the presence

 of solidified borax or similar colorless substances; Rarely diffusion of color or asterism.

Sapphire - Usually heated; Occasionally diffusion of color or asterism; Occasionally irradiation to

 provided temporary intense yellow or orange color.

Serpentine - Rarely dyed.

Spinel - None

Spodumene - Rarely irradiated green.

Sugelite - None

Tanzanite - Usually heated.

Topaz - Blue-Usually irradiated and often heated; Yellow/Orange-Occasionally irradiated;

 Pink/Red-Usually heated; Brown-None; Green-Usually irradiated.

Tourmaline - Chrome Vanadium-None; Cat's Eye-None; Yellow/Orange-Rarely heated or

 irradiated; Blue/Green-Commonly heated, Occasionally the penetration of colorless oil or

 unhardened resins into voids, Occasionally filling of surface cavities or fractures with a colorless

 hardened substance; Pink/Red/Purple-Occasionally heated, Commonly irradiated, Occasionally

 penetration of colorless oil or unhardened resins into voids, Occasionally filling of surface cavities or

 fractures with a hardened substance, Occasionally penetration of coloring agents into voids.

Turquoise - Commonly impregnated with plastic; Commonly impregnated with colorless oil or

 wax; Rarely dyed.

Zircon - Green/Brown-None; Yellow-Rarely heated; Blue/Red/Colorless- Always heated from the

 brownish crystals.