What are the treatments in Chalcedony? And how is this related to gem Green onyx, and Black Onyx?

Since at least 2000BC, Chalcedony has been subjected to heat treatment to create carnelian. Heat-treated agates were among the treasures unearthed from the tomb of King Tutankhamen (1300BC). Most of the carnelian currently on the market has been heating treated. Agate is quite porous and can be soaked in acid to create a dark outer layer in preparation for carving en cameo. Porosity also makes chalcedony a good candidate for dyeing. Dyeing will sometimes produce a very highly saturated unnatural-looking hue.

For example, “green onyx” is colorless chalcedony that has been dyed rich dark green; it looks simply too green to be true and it is! Black onyx is also universally dyed. The blue varieties of chalcedony are also subject to dyeing. Under magnification, natural color agate will usually show evidence of thin color bands. Specialists call these bands fortifications of color. Heat treatment will burn out the bands. The acid treatment produces a dark, dense, “burnt” look in Carnelian (Chalcedony). Many first-to third-century Roman intaglios, engraved seal stones, fit this description perfectly. Because agates are relatively reasonable in cost, treatment is almost never disclosed to the buyer.

Chalcedony color chart dyed
                                 Chalcedony color chart dyed

This section will consider the five most beautiful and commercially important varieties of chalcedony: 

  • Gem chrysocolla
  • Holley blue
  • Mojave blue agate
  • Carnelian
  • Chrysoprase.

    Only one color is natural in Chalcedony, the rest are dyed. But still, this stone is high in demand. Color remains stable, it does not fade with time. Not even small companies but also big jewelry companies are using this stone in their designs.


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It is important to take some general precautions if you are wearing jewelry made of Chalcedony. You should avoid harsh chemicals, thinner (paint remover). Chalcedony is quite porous like Turquoise and it easily absorbs chemicals. Make sure to not use it in extreme heat, it may affect the color. As with most gemstones, avoid the use of any harsh household chemicals (bleach, sulfuric acid, etc.) when caring for or cleaning chalcedony. Chalcedony is quite porous, which means that it can be easily stained and absorbs chemicals and colors very easily.

Writing Original articles by Navneet Gems and Minerals, the source of Wholesale Loose Chalcedony, Green Onyx and Black Onyx, and many more.