CHALCEDONY

Carnelian (chalcedony) and diamond ring, by Van Cleef & Arpels
Van Cleef & Arpels ring set with chalcedony
Species:  Chalcedony
Mohs Hardness:  7 out of 10
Color:  Varies depending on the variety.  Scroll down for more information.
RI:  1.535 to 1.539 (1.53 or 1.54 spot reading)
Birefringence:  Usually not detectable
SR/DR/AGG:  AGG
Spectrum:  Not diagnostic
Fluorescence:  Generally inert
SG:  2.60 (+0.10 / -0.05)
Routine Treatments:  None
Additional Enhancements:  Dyeing

Chalcedony Facts


Chalcedony is a microcrystalline form of quartz.

Chalcedony is a species of several different gems, such as agate, carnelian, sard, onyx, sardonyx, jasper, bloodstone, prase, chrysoprase, and more.

​Chalcedony can be dyed almost any color.

Chalcedony Varieties

AGATE
Agate
Close-up of agate

​Agate is chalcedony with curved or angular bands or layers.
BLOODSTONE
Macro photograph of the red
Close-up of bloodstone

Bloodstone is a dark green chalcedony, known as jasper, with red "blood splatter" inclusions.
CARNELIAN
Carved carnelian and marcasite scarf clip, in sterling silver
Carnelian & marcasite Art Déco Era Egyptian Revival scarf clip

Carnelian is the semi-transparent to semi-translucent, orangy red to brownish red or brownish orange variety of chalcedony.
CHRYSOPRASE
Vintage sterling silver, dyed green chalcedony & marcasite necklace
Vintage chrysoprase necklace

Chrysoprase is the semi-transparent to semi-translucent, light to medium-dark yellowish green variety of chalcedony.
JASPER
Vintage sterling silver ring set with red jasper.
Red jasper ring

Jasper is the general term for opaque chalcedony of any color other than black or specially-named chalcedonies.
ONYX
Vintage onyx and diamond cufflinks and studs set in 14 karat gold
Black onyx and diamond cufflinks and shirt studs set

Onyx is a banded variety of chalcedony.  While agate has curved bands, onyx has parallel bands.

These bands occur in white and nearly every color, except blue and purple.  Black and white alternating bands is common.
PRASE

Prase is the translucent to semi-translucent dark green variety of chalcedony.  Generally darker than chrysoprase with less color saturation.
SARD
A Victorian Era antique sard intaglio watch fob
A Victorian Era sard watch fob

Sard is the semi-transparent to semi-translucent, dark brownish red to orangy brown, to brown variety of chalcedony.  It's generally darker than carnelian with less color saturation.
SARDONYX
Vintage, German-made sardonyx and sterling necklace.
Banded sardonyx

Sardonyx is composed of alternating bands of either sard or carnelian with white onyx, black onyx, or both.

All photos courtesy of Scott Papper, GIA GG, AJP, CMA (NAJA)