Kyanite, Andalusite & Iolite

These gems are distinct studies in crystallography and optical physics.

Kyanite is an aluminium silicate known for an intense, sapphire-like blue. It is highly anisotropic in hardness: about 4.5 along the length of the crystal, and about 7 across its width.

Andalusite shares the chemical formula of kyanite (they are polymorphs) but crystallises in a different system. It is prized for strong pleochroism, showing a simultaneous interplay of olive green and reddish-brown (sometimes called its earthy colours) within the same faceted stone, depending on the viewing angle.

Iolite, the gem variety of cordierite, is sometimes called the Viking compass or water sapphire. It exhibits strong trichroism; a single iolite crystal can appear violet-blue from one direction, clear as water from another, and yellowish-brown from a third.

Shop the Kyanite collection Back to full encyclopedia