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>> Group(s) : silicates
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It was also known as "dichroïte" (because of its strong dichroism) or "iolite" (because of its purple color), the anglo-saxons still call it by that name. It honors the name of the French geologist Cordier, Professor at the National Museum of Natural History in Paris.
It was also called "compass stone" or "stone of the Vikings" because they had observed that it remained straight in the axis of the sun even though it was obscured by haze.

Exploited sites

It is widespread in the gneisses, in crystalline schists, in some granites but very rarely in beautiful crystals, only the transparent ones from Madagascar and Sri Lanka are considered gems.

See pictures of the mines / other pictures

Use in jewelry

It is cut in the axis which reinforces the most its blue color, in rectangular shape as the emerald or oval or round faceted, but it is rarely used, it is mostly a collection stone. It has been called the "water sapphire" but this name is prohibited.
Iolite is the stone of the 21st anniversary year of marriage.

Daily care and precautions

Although of a good hardness, it is sensitive to shocks that can cause its cleavage. Not to put in contact with acids.

Looking alike stones

amethyst , benitoite , kyanite , sapphire , spinel , tanzanite

Historical healing properties

It would be a gem of spirituality, initiation, but softer than sapphire and tanzanite. Associated with the throat chakra and front, it would provide a strong link between the earthly anchor and the cosmic mind. It would be intuitive, would avoid evil thoughts that might lead to depression.

Imitations and treatments

Glass imitations exist. Its strong pleochroism can easily differentiate it from imitations.

Chemical characteristics

magnesium aluminium silicate

Physical characteristics

Main color : blue

Other colors : purple

sometimes brown shades

Color of streak : white

Luster : vitreous, greasy

Hardness : 7.0 to 7.5

Density : 2.58 to 2.66

Cleavage : good

Fracture : conchoidal

Optical properties

Transparency : transparent

Refractive Index : 1.510 - 1.580

Double refraction : 0.010

Weak biaxial (-)

visible double refraction : yes

Dispersion : 0.017 (0.009)

Pleochroism : very strong

Number of colors : 3

Purple-blue, pale blue-gray, yellow-brownish

Absorption spectrum : 492 - 456

cordierite spectrum system

cordierite spectrum system

Fluorescence : none

Inclusions : numerous inclusions of goethite flakes, hematite and mica, which give it the brown shades


Short and well colored prisms


Crystal system : orthorhombic

Other informations

Astrological sign : Gemini, Libra, Pisces

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  • Gemini Gemini
  • Libra Libra
  • Pisces Pisces

It brings the right vision.