Iolite
Iolite is also called cordierite after the French Geologist Pierre Cordier. It is a blue to violet stone often deeply coloured when looking through the crown of a correctly oriented cut stone. Looking through the pavilion may show a colourless or yellowish stone. This is due to a strong trichroism and is the reason for iolite also being called water sapphire (a misleading description in the trade). Three colours or shades of colour are visible when viewing the stone from different directions.
Light is polarised through iolite, a feature employed by the Vikings to locate the sun through clouds on overcast days. Viewing the sky through an iolite crystal at sea revealed the suns exact position, assisting daytime navigation.
Properties of the Gemstone and Additional Information
| Gemstone type: | Iolite is also called cordierite by mineralogists. |
| Crystal System: | Orthorhombic |
| Chemical Composition: | A complex magnesium aluminium silicate, Mg2Al4Si5O18 |
| Colour: | Blue, violet. colourless are rare |
| Lustre: | Vitreous |
| Pleochroism: | Trichroic: Strong showing blue, violet and pale yellow to colourless |
| Dispersion: | Low |
| Hardness: | 7 to 7 1/2 on the Mohs' scale |
| Toughness: | Fair |
| Cleavage: | Indistinct |
| Density in gm/cc: | 2.57 to 2.61 |
| Double refraction: | Yes |
| Refractive index: | 1.54 to 1.56 |
Common Treatments
Iolite is not normally treated