Sard | Gemopedia

Sard is a translucent chalcedony that is light to dark reddish-brown. It is formed from the deposition of silica at low temperatures from silica-rich waters percolating through cracks and fissures in other rocks. Sard is darker and browner in tone than carnelian.
Colors
Dark Brownish Red To Orangy Brown To Brown

Sard Classification

Common Name

Sard

Species

Quartz

Variety

Chalcedony

Colors

Dark Brownish Red To Orangy Brown To Brown

Alternate Names

Gemstone Groups

Key Separations

RI, SG, appearance and fracture

Comments

sard is darker and less saturated in color than carnelian.

Sard 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

Sard Chemistry & Crystallography

Chemical Name

silicon dioxide (aka silica)

Chemical Formula

SiO2

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Polycrystalline

Comments

Sard Characteristic Physical Properties

Hardness

6.5-7

Streak

White

Specific Gravity

2.55-2.7 Typical:2.6

Toughness

Excellent

Inclusions

Luster

Vitreous

Stability

Good

Fracture

Conchoidal, Granular

Cleavage

None

Comments

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