Chalcedony

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 HISTORY and LORE

  • Though not familiar by name, an old and illustrious gem family. Treasured by humans since prehistoric times, chalcedonies were sacred and royal gemstones in early civilizations around the world.
  • Named for Chalcedon, an ancient trade center located in what is now Turkey.
  • Long used in Europe as a charm against ghosts.

 

VALUE FACTORS

  • Color: Range is almost unlimited. Many natural colors, and others from treatment.
  • Clarity: Translucent to opaque.
  • Cut: Cabochons, carvings, tablets, and beads in many shapes.
  • Size/Weight: many varieties are available in all sizes, and occur in pieces big enough for large carvings or other ornamental uses. (Normally not priced or sold by carat weight.)

 

TREATMENT

  • Often dyed, and in a wide variety of colors. Some techniques have been used since Roman times. The effects are normally permanent, and the treatment creates no special care requirements.

 

GEMOLOGY

  • A mineral species closely related to quartz. In fact, mineralogists consider it a quartz variety. Composed mostly of silicon and oxygen: chemical formula SiO2, which is the same as quartz.
  • Agate, bloodstone, carnelian, onyx, and sardonyx are well known chalcedony varieties. Others include:

             

             Amethystine chalcedony – purple

             Chrysocolla chalcedony – bright blue or blue-green

             Chrysoprase – light yellowish green

             Plasma – dark green with white or yellow spots

             Prase – dark green

             Sard – dark orange, brownish red, or brown

 

CARE

Chalcedony generally has good wearability.

  • Hardness: Moderate scratch resistance. Rates 6.5 to 7 on the Mohs Hardness Scale.
  • Toughness: Good resistance to chipping and breaking.
  • Stability: If dyed, color may eventually fade.
  • Cleaning: Liquid cleaner, or detergent and water. Ultrasonic is usually safe.

 

 

 

 

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