Comparison · Semi-Precious Stones
Iolite vs Tanzanite
Iolite and Tanzanite are easy to confuse because both are semi-precious stones. Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Iolite and Tanzanite
- Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Tanzanite feels noticeably heavier for its size (specific gravity 3.35 versus 2.6 for Iolite).
- They overlap in blue and purple, but Iolite also comes in gray.
Iolite vs Tanzanite properties
| Property | Iolite | Tanzanite |
|---|---|---|
| Type | Semi-Precious Stones | Semi-Precious Stones |
| Mohs hardness | 7 | 6.5 |
| Luster | vitreous | vitreous |
| Streak | White | White |
| Transparency | transparent | transparent |
| Specific gravity | 2.6 | 3.35 |
| Crystal system | orthorhombic | orthorhombic |
| Common colors | Violet-Blue, Blue, Gray | Blue, Violet, Purple |
| Rarity | uncommon | legendary |
| Typical specimen value | $30–$800+ | $300–$10000+ |
Which is more valuable?
Tanzanite is usually the more valuable of the two: a typical collector specimen runs about $1000 against $100 for Iolite, and premium Tanzanite can reach $10000 or more.
About Iolite
Iolite is the gem variety of cordierite, showing strong pleochroism—appearing different colors from different angles. Vikings may have used it for navigation.
About Tanzanite
Tanzanite is a blue-violet variety of zoisite found only in Tanzania. It's 1,000 times rarer than diamond and was only discovered in 1967.
Iolite vs Tanzanite FAQ
Is Iolite the same as Tanzanite?
No. Both are semi-precious stones, but they are distinct species with different hardness, streak or luster. Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Iolite from Tanzanite?
Both sit near Mohs 7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Tanzanite feels noticeably heavier for its size (specific gravity 3.35 versus 2.6 for Iolite). They overlap in blue and purple, but Iolite also comes in gray.
Which is harder, Iolite or Tanzanite?
Iolite is harder: Mohs 7 against Mohs 6.5 for Tanzanite.
Which is more valuable, Iolite or Tanzanite?
Tanzanite is usually the more valuable of the two: a typical collector specimen runs about $1000 against $100 for Iolite, and premium Tanzanite can reach $10000 or more.
