Forsterite | Gemopedia

Forsterite is a colorless to greenish transparent member of the olivine mineral family, which also includes peridot. Forsterite has a heavy magnesium chemical composition and large crystals are not common, but highly sought after by collectors.
Colors
Colorless, Green, Yellow Green, Yellow, White

Forsterite Classification

Common Name

Forsterite

Species

Forsterite

Variety

Colors

Colorless, Green, Yellow Green, Yellow, White

Alternate Names

Gemstone Groups

Olivine

Key Separations

RI and birefringence

Comments

Forsterite is in the olivine group with peridot. If the stone is bright green it is probably peridot if the stone is colorless it is forsterite.

Forsterite Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.635-1.671

Birefringence

0.034-0.035

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert to weak greenish yellow
LWUV: Inert to weak orangy white

CCF Reaction

Pleochroism

Dichroic, unobservable or weak, varying shades of body color

Dispersion

Strength: none

Comments

Forsterite Chemistry & Crystallography

Chemical Name

magnesium silicate

Chemical Formula

Mg2SiO4

Synthesis

Crystal System

Orthorhombic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Forsterite Characteristic Physical Properties

Hardness

6.5-7

Streak

White

Specific Gravity

3.23-3.26 Typical:3.2

Toughness

Poor

Inclusions

Luster

Vitreous

Stability

Fracture

Conchoidal

Cleavage

Good, in two directions

Comments

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