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Tanzanite vs Cubic zirconia

Cubic zirconia is harder (Mohs 8–8.5) than Tanzanite (Mohs 6–7), so it resists scratching better; Tanzanite is softer than quartz dust (7) and needs more care in everyday rings.

Cubic zirconia has the higher refractive index (2.15–2.18 vs 1.691–1.700), which a refractometer (over-the-limit reading) can use to separate them.

Cubic zirconia is denser (SG 5.8 vs 3.35); a cubic zirconia of the same size weighs about 73% more.

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PropertyTanzaniteCubic zirconia
Species / materialZoisiteSynthetic zirconium oxide
Mohs hardness6–78–8.5
Refractive index1.691–1.7002.15–2.18
Specific gravity3.355.8
Crystal systemOrthorhombicCubic
Birefringence0.008–0.013None (isotropic)

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

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