Semi-Precious Stones · uncommon
Iolite
Iolite is the gem variety of cordierite, showing strong pleochroism—appearing different colors from different angles. Vikings may have used it for navigation.
Also known as: viking compass, water sapphire.
Iolite properties at a glance
| Type | Semi-Precious Stones |
|---|---|
| Chemical formula | Mg2Al4Si5O18 |
| Mohs hardness | 7 |
| Crystal system | orthorhombic |
| Luster | vitreous |
| Streak | White |
| Cleavage | Good |
| Fracture | Conchoidal |
| Specific gravity | 2.6 |
| Transparency | transparent |
| Common colors | Violet-Blue, Blue, Gray |
| Rarity | uncommon |
Geology & background
Forms in high-grade metamorphic rocks and some igneous rocks.
Vikings may have used iolite as a polarizing filter to locate the sun on cloudy days for navigation.
How to identify Iolite
- Check whether the specimen's color and texture match typical Iolite examples.
- Photograph a fresh surface in natural light and avoid shadows, glare, or wet surfaces.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Full Iolite identification guide: checklist, home tests and look-alikes →
Iolite vs similar stones
Not sure it isn't something else? Side-by-side comparisons with the stones most often confused with Iolite.
Where Iolite is found
Iolite is reported from multiple localities or geological settings. Exact locality should be verified from specimen provenance, maps, or field notes.
How much is Iolite worth?
| Entry-level specimen | $30 |
|---|---|
| Typical collector specimen | $100 |
| Premium specimen | $800+ |
Value depends on size, condition, color, crystal quality, locality, rarity, preparation, and provenance. Treat this as educational guidance, not an appraisal.
Common uses
- Jewelry
- Collector specimens
Interesting facts
- Also called 'Viking's Compass' - may have been used for navigation
- Shows three different colors when viewed from different angles
- Sometimes called 'water sapphire'
Care & safety
Treat Iolite as a collector specimen unless hardness, cleavage, and fracture are confirmed.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a properly rated respirator.
Iolite FAQ
What is Iolite?
Iolite is the gem variety of cordierite, showing strong pleochroism—appearing different colors from different angles. Vikings may have used it for navigation.
How much is Iolite worth?
Entry-level Iolite specimens sell for around $30, a typical collector specimen for about $100, and premium pieces for $800 or more. Value depends on size, condition, color, crystal quality, locality, rarity, preparation, and provenance. Treat this as educational guidance, not an appraisal.
How hard is Iolite?
Iolite has a Mohs hardness of 7. It scratches glass and a steel knife and cannot be scratched by a steel file.
Where is Iolite found?
Notable sources of Iolite include India, Sri Lanka, Myanmar, Madagascar, and Brazil. Forms in high-grade metamorphic rocks and some igneous rocks..
What is Iolite used for?
Iolite is used for jewelry and collector specimens.
