Judging quality
Rotate the stone: dramatic color change confirms the identification. Cutters must orient carefully, so well-cut iolite showing full blue face-up is worth seeking.
Cordierite
Iolite
Strongly pleochroic cordierite that reads violet-blue from one direction and pale yellow-grey from another, all within a single crystal.
Care
Reasonably hard but cleaves. Warm soapy water.
History & lore
Often called the Viking compass stone, on the hypothesis that its polarising behaviour helped locate the sun under cloud.
Cultural history, recorded as tradition rather than as medical or scientific claim.
Common questions about Iolite
- What is Iolite?
- Strongly pleochroic cordierite that reads violet-blue from one direction and pale yellow-grey from another, all within a single crystal.
- How hard is Iolite and what is it made of?
- Iolite is a Cordierite-family mineral with the composition Mg2Al4Si5O18. It crystallizes in the orthorhombic system and rates 7-7.5 on the Mohs hardness scale. It occurs in violet-blue, grey.
- Where does Iolite come from?
- Notable localities for Iolite include India, Sri Lanka, Madagascar, Tanzania.
- How do you tell good Iolite from filler?
- Rotate the stone: dramatic color change confirms the identification. Cutters must orient carefully, so well-cut iolite showing full blue face-up is worth seeking.
- How do you care for Iolite?
- Reasonably hard but cleaves. Warm soapy water.
See it in person
Photographs only go so far
Both rooms are open six days a week, and there is always someone happy to pull pieces out of the case so you can compare them under the light.