Peridot | Gemopedia

August's birthstone, peridot, is a relatively inexpensive, beautiful gem with a pedigree dating back as far as early Egyptians. Among its accolades, peridot can count being a favorite among royals and clergy, used to adorn everything from a queen's crown to a knight's sword. Peridot jewels were actually among Cleopatra's beloved treasures, though she believed them to be emeralds, as gems were then classified solely by color. Prized for its all natural, unenhanced range of colors, peridot is the gem variety of olivine and exhibits colors ranging from golden lime greens to rich grass greens.
Alternate
Names
Chrysolite, Hawaiite
Colors
Green, Greenish Yellow, Brownish Green

Peridot Classification

Common Name

Peridot

Species

Forsterite

Variety

Colors

Green, Greenish Yellow, Brownish Green

Alternate Names

Chrysolite, Hawaiite

Gemstone Groups

Olivine

Key Separations

refractive index, birefringence, optic character, spectrum and possibly magnification. High birefringence results often in very visible doubling of back facets under magnification.

Comments

Crystal habit is commonly an orthorhombic prism with vertical rhombic faces and side pinacoids. Peridot is a member of the olivine isomorphous series with forsterite (magnesium silicate) and fayalite (iron silicate) as the end members. Misnomers: evening emerald or night emerald. August birthstone.

Peridot Optical Properties

Transparency

Transparent

Refractive Index

1.654-1.69
Tolerance:(+0.020/-0.020)

Birefringence

0.035-0.038

Optic Character

Biaxial

Optic Sign

Positive or Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Dichroic, unobservable or weak, varying shades of body color

Dispersion

Comments

Peridot Chemistry & Crystallography

Chemical Name

magnesium iron silicate

Chemical Formula

(Mg,Fe)2SiO4

Synthesis

Crystal System

Orthorhombic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Peridot Characteristic Physical Properties

Hardness

6.5-7

Streak

White

Specific Gravity

3.27-3.38 Range:0.04/-0.07 Typical:3.34

Toughness

Varies

Inclusions

Peridot is a type II clarity stone. Peridot might contain black octahedral chromite crystals. Stones might have liquid and gas inclusions that sometimes cause stress cracks that have a disk-like or "lily pad" appearance. Stones occasionally have mica flakes that give the stone a brownish hue. Stones from Pakistan often contain black ludwigite inclusions that have a hair or rod-like appearance.

Luster

Vitreous

Stability

Fair

Fracture

Conchoidal

Cleavage

Good, in two directions

Comments

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