Identification guide · Semi-Precious Stones
How to Identify Tanzanite
Tanzanite is usually blue, violet, and purple with a vitreous luster and is transparent. It has a Mohs hardness of 6.5. It scratches glass and a steel knife and cannot be scratched by a steel file. Its streak is white. It is most often confused with Spinel, Iolite, and Zoisite; the tests below separate them.
Tanzanite identification checklist
| Color | Blue, Violet, Purple | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Transparent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6.5 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect | |
| Fracture | Uneven | |
| Specific gravity | 3.35 | Heavier than it looks (specific gravity about 3.35). |
| Crystal system | Orthorhombic |
Tanzanite look-alikes and how to tell them apart
Spinel is harder (Mohs 8) than Tanzanite (Mohs 6.5), so Spinel will scratch Tanzanite and not the other way round. It scratches glass and a steel knife and cannot be scratched by a steel file. Tanzanite vs Spinel →
Both sit near Mohs 6.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Tanzanite vs Iolite →
Both sit near Mohs 6.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Tanzanite vs Zoisite →
Aquamarine is harder (Mohs 7.5) than Tanzanite (Mohs 6.5), so Aquamarine will scratch Tanzanite and not the other way round. It scratches glass and a steel knife and cannot be scratched by a steel file.
Is my Tanzanite real?
- Hardness: real Tanzanite sits at Mohs 6.5. Glass imitations are about 5.5, so genuine Tanzanite scratches glass while a glass fake cannot.
- Bubbles: round gas bubbles under a 10x loupe mean glass or resin, never a natural stone.
- Color: dyed material concentrates color in cracks and pores; look for pigment collecting at the edges of fractures.
- Temperature: natural crystals feel cool and take longer to warm in your hand than plastic or resin.
Field tips
- Check whether the specimen's color and texture match typical Tanzanite examples.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Tanzanite identification FAQ
How can you tell if a rock is Tanzanite?
Check the color (blue, violet, and purple), the vitreous luster, a Mohs hardness of 6.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Tanzanite?
Tanzanite has a Mohs hardness of 6.5. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Tanzanite and Spinel?
Tanzanite (Mohs 6.5, vitreous luster) and Spinel (Mohs 8, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Tanzanite vs Spinel comparison for a side-by-side table.
How do I know if my Tanzanite is real?
Real Tanzanite matches the hardness listed above, shows no round gas bubbles under magnification, and does not concentrate dye in cracks. Glass and resin fakes fail at least one of those checks.
Is Tanzanite worth anything?
Entry-level Tanzanite specimens sell for around $300, typical collector pieces about $1000, and premium examples $10000 or more depending on size, quality and locality.
What color is Tanzanite?
Tanzanite is most often blue, violet, and purple. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
