Onyx is a form of chalcedony and is found worldwide in colors of grey, brown, white and black. However, almost all black onyx is dyed to increase it's depth of color and often stones sold as black onyx are actually dyed agate since natural onyx is brittle and known to chip and scratch easily. One method of changing the appearance is to soak the agate in a sugar solution and then heat it in a sulfuric acid solution to carbonize the sugar particles. More onyx information and facts.
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