Fire Agate | Gemopedia

Fire Agate is one of those gems whose beauty and appeal is hard to describe with mere words. A phenomenal gem, it is an opaque variety of chalcedony that exhibits a colorful iridescence. The iridescence is caused by layers of silica and iron oxides, which interfere with the passage of light. Diffraction causes the colorful metallic hues that make this gemstone a favorite of collectors. Its brown body color is also a result of the iron oxide content. Gem quality fire agate is by far rarer than diamonds, emeralds or rubies and is as colorful as any precious Australian opal, although it is typically sold at a fraction of the cost.
Colors
Dark Reddish Brown

Fire Agate Classification

Common Name

Fire Agate

Species

Quartz

Variety

Chalcedony

Colors

Dark Reddish Brown

Alternate Names

Gemstone Groups

Key Separations

RI, SG, appearance and structure

Comments

The iridescent effect is caused by light bouncing off the limonite and goethite inclusions.

Fire Agate Optical Properties

Transparency

Semitranslucent - 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

Pleochroism

None

Dispersion

Strength: none

Comments

Fire Agate Chemistry & Crystallography

Chemical Name

silicon dioxide (aka silica)

Chemical Formula

SiO2

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Polycrystalline

Comments

Fire Agate Characteristic Physical Properties

Hardness

6.5-7

Streak

Specific Gravity

2.55-2.7 Typical:2.6

Toughness

Excellent

Inclusions

Fire agates iridescent colors and botryoidal growth structure make it distinctive.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal

Cleavage

None

Comments

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