Seylan Gems & Jewelry
Iolite is the gem name for cordierite. Turn it and the color can swing from violet-blue to a gray or yellow-brown. That pleochroism is the feature. It is also why a single photo can mislead you.
Specifications
Typical published ranges used in gemology. Specific gravity below matches our carat calculator default where applicable. (SG 3.00)
| Hardness (Mohs) | 7–7.5 |
|---|---|
| Refractive index | About 1.54–1.55 |
| Optic character | Doubly refractive, strongly pleochroic |
| Specific gravity | About 2.61 |
| Chemistry | Cordierite, a magnesium aluminum silicate |
| Lustre | Vitreous |
A well-cut iolite puts the violet-blue direction through the face. If the table is oriented the other way, the stone looks gray and the listing photo may still have caught the blue flash. Use every photo and any 360 view.
“Water sapphire” is an old trade nickname. The mineral is not corundum. Hardness, density, and price follow iolite, not sapphire.
Hardness around 7 is acceptable for careful jewelry. There is cleavage, so a hard knock can split a thin stone more easily than the hardness number suggests. No ultrasonic cleaner if the stone is included.
That is the spelling on our category. The gem is iolite. The link still opens that category.
No. Sapphire is corundum, hardness 9. Iolite is cordierite.
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