chalcedony

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Carnelian (chalcedony) and diamond ring, by Van Cleef & Arpels

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)

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.

agate

Close-up of agate

​Agate is chalcedony with curved or angular bands or layers.

bloodstone

Close-up of bloodstone

Bloodstone is a dark green chalcedony, known as jasper, with red "blood splatter" inclusions.

carnelian

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 chrysoprase necklace

Chrysoprase is the semi-transparent to semi-translucent, light to medium-dark yellowish green variety of chalcedony.

jasper

Red jasper ring

Jasper is the general term for opaque chalcedony of any color other than black or specially-named chalcedonies.

onyx

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

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

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)