Chalcedony | Gemopedia

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).
Colors
Bluish To Whitish To Gray, Almost Any Color If Dyed

Chalcedony Classification

Common Name

Chalcedony

Species

Quartz

Variety

Colors

Bluish To Whitish To Gray, Almost Any Color If Dyed

Alternate Names

Gemstone Groups

Key Separations

RI, SG, appearance and fracture. Color filter if dyed.

Comments

Misnomers: black onyx is black dyed chalcedony, green onyx is dyed green chalcedony, moonstone for milky chalcedony.

Chalcedony Optical Properties

Transparency

Semitransparent - Opaque

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

Dyed blue: appear red or pinkish: dyed green: light grayish to reddish or pinkish

Pleochroism

None

Dispersion

Strength: none

Comments

Chalcedony Chemistry & Crystallography

Chemical Name

silicon dioxide (aka silica)

Chemical Formula

SiO2

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Polycrystalline

Comments

Chalcedony Characteristic Physical Properties

Hardness

6.5-7

Streak

White

Specific Gravity

2.55-2.7 Typical:2.6

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

Stability

Good

Fracture

Conchoidal, Granular

Cleavage

None

Comments

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