Sardonyx | Gemopedia

Sardonyx is a form of onyx that is made up of bands of red sard and white chalcedony. Because of its banded patterns, sardonyx has been used for years in making cameos.
Colors
Carnelian, Sard Colors With Either White, Black Banding

Sardonyx Classification

Common Name

Sardonyx

Species

Quartz

Variety

Chalcedony

Colors

Carnelian, Sard Colors With Either White, Black Banding

Alternate Names

Gemstone Groups

Key Separations

RI, SG, appearance and fracture

Comments

Sardonyx Optical Properties

Transparency

Semitransparent - Semitranslucent

Refractive Index

1.535-1.539

Birefringence

0.004-0.004

Optic Character

Uniaxial

Optic Sign

Positive

Polariscope Reaction

Aggregate (AGG)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

None

Dispersion

Strength: none

Comments

Sardonyx Chemistry & Crystallography

Chemical Name

silicon dioxide (aka silica)

Chemical Formula

SiO2

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Polycrystalline

Comments

Sardonyx Characteristic Physical Properties

Hardness

6.5-7

Streak

White

Specific Gravity

2.55-2.7 Typical:2.6

Toughness

Excellent

Inclusions

Sardonyx has white and/or black bands alternating on carnelian or sard colors and this is what separates sardonyx from other calcedonies.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal, Granular

Cleavage

None

Comments

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