Chalcedony

 

Free Form Designer Agate Cabochon

Chalcedony is a mineral made up mostly of Silicon Dioxide and is a cryptocrystalline variety of quartz. Chalcedony comes in many forms and is essentially a term for a group of semi precious gemstones, rather than a single stone. Chalcedony and its variants are considered among the most beautiful stones in the world and have a hardness rating of generally between 6.5 and 7 on the Mohs Hardness Scale.



Free Form Designer Chrysoprase Cabochon

The name 'Chalcedony' comes from the Latin word chalcedonius. However it is also believed that the original Latin word and the current usage of the name 'Chalecdony' derive from an ancient Greek settlement in Asia Minor. This settlement was originally known as Chalkedon, but the modern English interpretation of the settlement is Chalcedon - hence the spelling of the name 'Chalcedony'.  

 

Free Form Designer Agate Cabochon

 

This particular gemstone group has been used as long as humans have been utilising their surrounding materials. Some of the earliest and most primitive human tools that have been discovered have been made of various types of Chalcedony.

Chalcedonies are found in an immense array of colours including, black, blue, brown, colorless, gray, green, orange, red, violet, white, yellow, or any combination of these. 

Green Chalcedony with Minor Dendrites

 

Because of the vast array of varieties, the use of chalcedony eventually extended to that of decorative items. Native Americans for instance believe Chalcedony to be a sacred stone and it is used for ceremonial purposes. They believe that Chalcedony promotes stability within each tribe.

  

35mm x 18mm Heliotrope (Bloodstone)
Cabochon

As stated above, Chalcedony is essentially a term used to describe a broader group of gemstones which varies widely in colour and appearance. The most notable members of this group include gemstones such as Agate, Carnelian, Heliotrope (Bloodstone), Chrysoprase, Aventurine and Onyx, but has many other members as well. Chalcedony deposits in its various forms are found worldwide, with particular areas being known for or associated with the individual forms of chalcedony.

From a Lapidary Point of View
Because of the endless range of chalcedony forms, this particular stone is always going to please. From the Banding of Agates, through to the rich apple green of chrysoprase, to the spotted nature of Heliotrope, there is always going to be something of interest in a Lapidary sense. Some of the most eye catching and beautiful cabochons that I have cut have been some form of chalcedony or another. Most chalcedonies are at the harder end of the scale (with a Mohs rating of generally 6.5 to 7) and the compact crystalline structure of the material results in a beautiful mirror like finish. It is not surprising then that most lapidaries are more than happy to cut this material, and I am certainly no exception.

Free Form Designer Banded Agate Cabochon

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