Iolite
Iolite is the gem variety of cordierite, showing strong pleochroism—appearing different colors from different angles. Vikings may have used it for navigation.
.jpg?width=760)
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.
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.
.jpg?width=320)
.jpg?width=320)
