Heating and Irradiation are done to change color, enhance color, remove inclusions/improve clarity.
Here is a short list of minerals and the purpose for treatment.
AMBER Deepen color and produce ‘sun spangles’ inside the amber.
AMETHYST Lighten or darken the purple color, change color to yellow/orange, which is renamed to CITRINE or change color to green, which is renamed to PRASIOLITE.
AQUAMARINE Change from green to blue or remove any green and yellow areas/tints to achieve pure blue
CARNELIAN Change color from brown-yellow to orange-red.
KUNZITE Change color from purple to blue or from green to pink or violet.
MORGANITE Change color from orange to pink.
ROCK QUARTZ Quartz that is clear or white in color. Change color to brown/caramel, green, orange, purple, and yellow and/or increase clarity.
RUBY Change color from purple to red and/or increase clarity.
SAPPHIRE Enhance/deepen color and/or increase clarity.
SMOKY QUARTZ Lighten color or change color to yellow/orange, which is renamed to CITRINE.
SPODUMENE Change color from purple to blue or from green to pink or violet.
TOPAZ Change color from yellow to pink. To change colorless to blue.
TOURMALINE Change color from dark green to emerald green. To change dark brown to light brown.
YELLOW TIGER'S EYE Change color from yellow to red.
ZOISITE To change color to from brown/yellow color to bluish purple and renamed TANZANITE. Almost all tanzanite on the market are the result of heat treatment. Natural deep blue Tanzanite exists, but is very rare.