Chalcedony

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Chalcedony is a broad gemstone family of many varieties of cryptocrystalline quartz gemstones. Chalcedony usually has a waxy luster and appears in a great variety of colors including blue, white, buff, tan, green, red, gray, black, yellow or brown. Different colored varieties of chalcedony have individual names including agate (banded), bloodstone (green with red spots), chrysoprase (apple green), carnelian (orange to red), flint (dull gray to black), jasper (spotted red, yellow, brown or green) and sard (light to dark brown).

Chalcedony Polished
Chalcedony Classification
Common Name Chalcedony
Species Quartz
Chalcedony Optical Properties
Transparency Semitransparent - Opaque
Dispersion Strength: None
Refractive Index 1.535-1.539
Birefringence 0.004
Optic Character Uniaxial
Optic Sign Positive
Polariscope Reaction Aggregate (AGG)
Fluorescence SWUV: Inert
LWUV: Inert
CCF Reaction Dyed blue: appear red or pinkish: dyed green: light grayish to reddish or pinkish
Pleochroism None
Chalcedony Characteristic Physical Properties
Hardness 6.5-7
Streak White
Specific Gravity 2.550-2.700 Typical:2.600
Toughness Excellent
Inclusions Chalcedony is frequently dyed so look for dye concentrations. Dyed green chalcedony is evenly colored slightly blueish green and will lack dye concentrations.
Luster Vitreous, Greasy
Stability Good
Fracture Conchoidal, Granular
Cleavage None
Chalcedony Chemistry & Crystallography
Chemical Name silicon dioxide (aka silica)
Chemical Formula SiO2
Crystal System Trigonal
Chemistry Classification Silicate

Chalcedony Colors

  • Black Chalcedony Black
  • Yellow Chalcedony Yellow
  • White Chalcedony White
  • Red Chalcedony Red
  • Purple Chalcedony Purple
  • Pink Chalcedony Pink
  • Orange Chalcedony Orange
  • Multi-color Chalcedony Multi-color
  • Green Chalcedony Green
  • Gray Chalcedony Gray
  • Brown Chalcedony Brown

Chalcedony Spectra

Chalcedony Spectra
DYED CHALCEDONY

Color due to chromium salts. A colorless milky grey chalcedony is dyed and cut as cabochons or sometimes faceted as seen here. A series of faint absorption bands of various widths are seen here centered at 580nm., 610nm., 630nm.640nm., and 665nm

Jewelry Television acknowledges the significant scientific contributions of John S Harris, FGA to the study of gemstone spectra and with deep appreciation to him, acknowledges the use of his images and related notes about gemstones and their spectra in the educational materials on this website.

Countries of Origin

Tanzania, United Republic Of; Colombia; United States of America (the); Uruguay; Madagascar; Kenya; Thailand; India; Turkey; Unknown; China; Namibia; Russian Federation (the); Brazil; Poland; Australia; Peru; Indonesia

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Species/Variety

Black Onyx

Black onyx is chalcedony that has been dyed or sugar-acid treated.

Black Onyx Chalcedony
Black Onyx Classification
Common Name Black Onyx
Black Onyx Optical Properties
Dispersion None
Birefringence 0.004
Black Onyx Characteristic Physical properties
Specific Gravity 2.55
Toughness Good
Stability Good

Sardonyx

Sardonyx is a form of onyx that is made up of bands of red sard and white chalcedony. Because ofits banded patterns, sardonyx has been used for years in making cameos.

Sardonyx Chalcedony
Sardonyx Classification
Common Name Sardonyx
Sardonyx Characteristic Physical properties
Inclusions Sardonyx has white and/or black bands alternating on carnelian or sard colors and this is what separates sardonyx from other calcedonies.

Chrome Chalcedony

Chrome chalcedony contains chromium, normally seen in the most coveted gems in the world; namely alexandrite, emerald and ruby. Present in small amounts, chromium gives these stones their unique shades of green, which have been compared to green seawater. Chrome chalcedony is usually untreated, as absolutely nothing is required to make this stone desirable! Although chrome chalcedony somewhat resembles chrysoprase in appearance, the two receive their color from two different elements.

Chrome Chalcedony Chalcedony
Chrome Chalcedony Classification
Common Name Chrome Chalcedony
Chrome Chalcedony Optical Properties
CCF Reaction Light grayish pink or reddish
Chrome Chalcedony Characteristic Physical properties
Inclusions Chrome chalcedony might contain black chromite crystals. Look for lack of dye concentrations to separate from dyed chalcedony.

Amethystine Chalcedony

Also referred to as "damsonite," amethystine chalcedony is an opaque to semi-translucent variety that is, you guessed it, purple. As chalcedony is technically a quartz, this gem is much like traditional amethyst and even can be heat treated to become a yellowish orange citrine color.

Amethystine Chalcedony Chalcedony
Amethystine Chalcedony Classification
Common Name Amethystine Chalcedony

Plasma

Plasma is the term for a deep green chalcedony that often shows small yellow, red or white spots.

Plasma Chalcedony
Plasma Classification
Common Name Plasma
Plasma Optical Properties
Dispersion None
Refractive Index 1.535-1.539
Birefringence 0.004
Pleochroism None
Plasma Characteristic Physical properties
Specific Gravity 2.55
Inclusions Plasma is dark green with white or yellowish spots.The stones semi transparent to opaque nature is what separates plasma from other chalcedony varieties.

Material Combination

Chrysocolla-In-Chalcedony

Chrysocolla forms as a decomposition product of copper minerals and frequently is intergrown with other minerals, in this case, with chalcedony. Also referred to as "gem silica," it is one of the rarest and most treasured variety of chalcedony. The gem may be seen in blue to blue-green color, and may be opaque to almost transparent.

Chrysocolla-In-Chalcedony Chalcedony
Chrysocolla-In-Chalcedony Classification
Common Name Chrysocolla-In-Chalcedony
Chrysocolla-In-Chalcedony Optical Properties
Pleochroism Unobservable
Chrysocolla-In-Chalcedony Characteristic Physical properties
Inclusions Chrysocolla-in-chalcedony might be unevenly colored.
Tim Matthews

Author

Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.