Prase | Gemopedia

Prase is a dull green to yellowish green variety of chalcedony, a cryptocrystalline quartz. It is commonly fashioned en cabochon to show off its leek-green color. Prase can be confused with chrysoprase since they are very similar in appearance, but a darker, less saturated color is typically indicative of prase.
Colors
Dark Green With White, Yellowish Spots

Prase Classification

Common Name

Prase

Species

Chalcedony

Variety

Prase

Colors

Dark Green With White, Yellowish Spots

Alternate Names

Gemstone Groups

Key Separations

RI, SG, appearance and fracture

Comments

Prase is less saturated in color than chrysoprase and its translucent to semi transparent nature separates it from plasma.

Prase Optical Properties

Transparency

Transparent - 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

Prase Chemistry & Crystallography

Chemical Name

silicon dioxide (aka silica)

Chemical Formula

SiO2

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Polycrystalline

Comments

Prase Characteristic Physical Properties

Hardness

6.5-7

Streak

White

Specific Gravity

2.55-2.7 Typical:2.6

Toughness

Excellent

Inclusions

Prase's green color is due to chlorite inclusions, the grayish green color is due actinolite fibers and the blue color is due to crocidolite fibers.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal, Granular

Cleavage

None

Comments

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