Gemstone profile and identification guide
Tanzanite is one of the few gemstones whose identity is closely tied to a single modern locality. Its blue-to-violet colour and pleochroic character give it an instantly contemporary profile among transparent jewellery stones.
Tanzanite is one of the few gemstones whose identity is closely tied to a single modern locality. Its blue-to-violet colour and pleochroic character give it an instantly contemporary profile among transparent jewellery stones.
Did you know? Commercial tanzanite is associated with a limited source area in Tanzania, which is why locality is part of its identity.
Use this profile as a collector reference and educational guide for quick on-page comparison, then validate with the interactive identification system.
Name: Tanzanite
Scientific classification: Sorosilicate (Zoisite Variety)
Hardness: 6.5 Mohs
Transparency: transparent
Lustre: vitreous
Crystal system: Orthorhombic
Primary colour: Blue
Secondary colour: Green
Colour family: Blues & Cyans
Observe the blue-violet range carefully and compare under different orientations if possible, since pleochroism is part of its character. It is often compared with sapphire or iolite but usually reads softer and more violet.
Status: verified-core-fields
Reference priority: GIA, Gem-A, Mindat, International Gem Society
Core identity fields reviewed against consensus gemological references (GIA/Gem-A/Mindat/IGS).
Some market- and locality-level details may still require citation-grade source notes for publication workflows.
Hardness category: medium
Hardness value: 6.5 Mohs
Chemical composition: Calcium aluminum hydroxy sorosilicate [Ca2Al3(SiO4)(Si2O7)O(OH)]
Crystal system: Orthorhombic
Common locations: Tanzania (Merelani Hills, Simanjiro District)
Learn more: Gem-A gemstone education resources.
Tanzanite sits in the blues & cyans grouping here, usually reading first as blue with green appearing as a secondary note or modifier.
Optical effects: Trichroism
Mineral species: Zoisite (tanzanite variety)
Mineral group: Epidote group (zoisite)
Chemical formula: Calcium aluminum hydroxy sorosilicate [Ca2Al3(SiO4)(Si2O7)O(OH)]
Mohs hardness: 6.5
Crystal system: Orthorhombic
Lustre: vitreous
Transparency: transparent
Streak: White
Cleavage: Perfect in one direction
Fracture: Uneven to brittle
Specific gravity: 3.30-3.38
Refractive index: 1.69-1.70
Optical phenomena: Trichroism
Colour range: Blue, Green, Brown, Purple, Violet
Common inclusions: Needle-like inclusions, healed fractures, growth zoning
Geological environment: Tanzanite occurs in Metamorphic rocks in the Neoproterozoic Mozambique Belt. Its Orthorhombic structure reflects the pressure-temperature conditions of those host rocks, with notable occurrences in Tanzania (Merelani Hills, Simanjiro District).
Principal mining regions: Tanzania (Merelani Hills, Simanjiro District)
Important commercial sources: Gem-quality tanzanite is commercially sourced only from the Merelani Hills in Tanzania
Historical significance: Discovered in the 1960s and marketed globally as a single-source gemstone from Tanzania.
Common treatments: Heat treatment is routine to shift brownish rough toward blue-violet.
Synthetic or imitation forms: No widely commercial synthetic tanzanite; glass and synthetic corundum are used as imitations.
Common look-alikes: Iolite, sapphire, synthetic spinel
Jewellery uses: Tanzanite is used chiefly for Often best in pendants, earrings, collector cuts, and occasional-wear rings that showcase colour without unnecessary risk.. In the trade it is commonly fashioned as faceted stones, calibrated cuts, and higher-clarity collector pieces, with Mohs hardness 6.5 guiding suitable jewellery applications.
Care recommendations: Tanzanite should be cleaned with lukewarm water, mild soap, and a soft brush. At Mohs 6.5 in the Orthorhombic system, avoid steam cleaners, harsh chemicals, and high-impact wear. Protect cleavage directions from sharp knocks during wear and setting.
Cross-check profile data with GIA Gem Encyclopedia and Mindat entry for Tanzanite.
Tanzanite is a Zoisite (tanzanite variety) material with chemistry Calcium aluminum hydroxy sorosilicate [Ca2Al3(SiO4)(Si2O7)O(OH)]. It develops in Metamorphic rocks in the Neoproterozoic Mozambique Belt, and economically significant production is associated with Tanzania (Merelani Hills, Simanjiro District).
Gem-quality tanzanite is commercially sourced only from the Merelani Hills in Tanzania
Best for: Tanzanite is used chiefly for Often best in pendants, earrings, collector cuts, and occasional-wear rings that showcase colour without unnecessary risk.. In the trade it is commonly fashioned as faceted stones, calibrated cuts, and higher-clarity collector pieces, with Mohs hardness 6.5 guiding suitable jewellery applications.
Ideal uses: Often best in pendants, earrings, collector cuts, and occasional-wear rings that showcase colour without unnecessary risk.
Tanzanite should be cleaned with lukewarm water, mild soap, and a soft brush. At Mohs 6.5 in the Orthorhombic system, avoid steam cleaners, harsh chemicals, and high-impact wear. Protect cleavage directions from sharp knocks during wear and setting.
Need another candidate? Use advanced gemstone search or return to the identification guide.
Compare hardness (6.5 Mohs), crystal system (Orthorhombic), colour profile, and lustre (vitreous) with your sample. Then cross-check related gemstones listed above.
Tanzanite sits in the blues & cyans grouping here, usually reading first as blue with green appearing as a secondary note or modifier.
Often best in pendants, earrings, collector cuts, and occasional-wear rings that showcase colour without unnecessary risk.. For maintenance, follow the care guidance in this profile.
GIA: general gemstone identity (reviewed) - Reviewed as a direct core gemstone profile.
Gem-A: gemological education and terminology (reviewed) - Reviewed as a direct core gemstone profile.
Mindat: mineral species and locality index (reviewed) - Reviewed as a direct core gemstone profile.
International Gem Society: collector-facing gem reference (reviewed) - Reviewed as a direct core gemstone profile.
