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Tourmaline vs Tanzanite

Tourmaline is harder (Mohs 7–7.5) than Tanzanite (Mohs 6–7), so it resists scratching better; Tanzanite is softer than quartz dust (7) and needs more care in everyday rings.

Tanzanite has the higher refractive index (1.691–1.700 vs 1.624–1.644), which a refractometer can use to separate them.

Tanzanite is denser (SG 3.35 vs 3.06); a tanzanite of the same size weighs about 9% more.

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PropertyTourmalineTanzanite
Species / materialTourmalineZoisite
Mohs hardness7–7.56–7
Refractive index1.624–1.6441.691–1.700
Specific gravity3.063.35
Crystal systemTrigonalOrthorhombic
Birefringence0.014–0.0210.008–0.013

Values are typical ranges from standard gemmological references; individual stones can vary.

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