"Chalcedony" is an umbrella term for a specific variety of quartz called microcrystalline which means that it is composed of tiny crystals that cannot be seen with the naked eye. Chalcedony is normally translucent to semi-transparent, and often has a milky color. It also comes in many colors, mostly red, black, purple, green, turquoise, yellow, orange and brown.
Carnelian, agate, bloodstone, flint, jasper and petrified wood are just a few examples of chalcedony.
Chalcedony is typically porous, so light colored chalcedony, in particular, can be dyed just about any color. The process involves the use of strong acids to “open the pores.” Then the chalcedony is submitted to a variety of repeated and prolonged immersions in metallic compound solutions that impart color. Reds, oranges and yellows are placed in iron oxide compounds; greens in chromium compounds; blues in cobalt compounds.
Chalcedony has been dyed to resemble other gemstones like lapis lazuli and chrysoprase. Sometimes chalcedony is bleached before dyeing it in order better to achieve a desired color. Chalcedony has also been changed by heating, giving the stone a reddish tone.
You can find chalcedony all over the world, although some regions are better known than others for the production of high quality chalcedony. Almost all the states of United States produce this stone. Other countries are Uruguay, India, Madagascar, Myanmar (Burma), Mexico, Brazil and Southwestern Africa.
So to answer my original question, chalcedony does come in many colors and the lighter stone can treated to create more brilliant colors. How do you know if the color of the stone is natural or dyed? From what I have read, it is difficult to distinguish natural from dyed chalcedony. In the end, dyeing the stone does not take away from its value.
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