Iolite | Gemopedia

Iolite is the gem-quality blue or blue-violet variety of cordierite. While iolite enjoyed popularity in jewelry in 18th-century Europe, this naturally beautiful gemstone is relatively new to today's jewelry market, and is regaining popularity with the public. Because of its varying levels of hardness and strong pleochroism, iolite is one of the most difficult stones for lapidaries to fashion. It must be cut in certain directions to take advantage of the best color, which can be tough when the shape of the rough doesn't lend itself to cutting in that same direction.
Alternate
Names
Cordierite, Dichroite, Bloodshot Iolite
Colors
Violet Through Slighty Violetish Blue, Rarely Colorless

Iolite Classification

Common Name

Iolite

Species

Cordierite

Variety

Iolite

Colors

Violet Through Slighty Violetish Blue, Rarely Colorless

Alternate Names

Cordierite, Dichroite, Bloodshot Iolite

Gemstone Groups

Key Separations

visible pleochroism, refractive index, birefringence and optic character. Eye visible pleochroism.

Comments

Misnomer: water sapphire.

Iolite Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.542-1.551
Tolerance:(+0.045/-0.011)

Birefringence

0.008-0.012

Optic Character

Biaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Trichroic, violet, colorless to yellow, and light grayish blue

Dispersion

Strength: moderate fire Value: 0.017

Comments

Iolite Chemistry & Crystallography

Chemical Name

magnesium aluminum silicate

Chemical Formula

Mg2Al4Si5O18

Synthesis

Crystal System

Orthorhombic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Iolite Characteristic Physical Properties

Hardness

7-7.5

Streak

White

Specific Gravity

2.56-2.66 Range:+/-0.05 Typical:2.61

Toughness

Fair

Inclusions

Iolite is a type II clarity stone. Sometimes apatite, hematite, iron oxide, magnetite, mica and rutile, inclusions are seen. Bloodshot iolite is the adventuresent variety with red plate like hematite, iron oxide inclusions along with goethite.

Luster

Vitreous

Stability

Fair

Fracture

Conchoidal, Uneven

Cleavage

Good, in one direction, Poor, in two directions

Comments

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