orthorhombic Sorosilicates
Tanzanite
Ca2Al3(SiO4)(Si2O7)O(OH):V
Quick Facts
Hardness
6.5
Specific Gravity
3.1
Refractive Index
1.691
Optical Character
Biaxial +
Crystal Structure
#! Species: Tanzanite (Zoisite)
#! System: Orthorhombic (mmm)
#! Habit: Prismatic with extreme trichroism
orthorhombic[mmm]:{100}@1.0[pleochroism:strong] + {010}@0.9 + {001}@1.2 + {110}@0.7
orthorhombic
mmm
{100} {010} {001} {110}
Physical Properties
Crystal Systemorthorhombic
Hardness (Mohs)6.5
Specific Gravity3.1
CleavagePerfect in one direction
FractureUneven to conchoidal
LustreVitreous
Optical Properties
Refractive Index1.691
Birefringence0.008-0.013
Optical CharacterBiaxial +
Dispersion0.021
Pleochroismvery strong: Blue / Purple / Bronze-brown (Strongest trichroism of any common gemstone; all three colours distinctly different)
Colours
Violet-blueBluePurpleBurgundy (untreated)
Localities
Tanzania (Merelani Hills)
Common Inclusions
Growth tubesNegative crystalsFingerprint inclusionsStress cracks (from cleavage)
Known Treatments
Heat treatment (universal, removes brown)
Crystal Forms
prismpinacoid
Diagnostic Features
Extremely strong trichroism (blue/purple/bronze); heat treatment converts brown to blue-violet
Interactive Preview
Open this crystal in the CDL Playground to rotate, export, and explore in 3D.
Open in Playground #! Species: Tanzanite (Zoisite)
#! System: Orthorhombic (mmm)
#! Habit: Prismatic with extreme trichroism
orthorhombic[mmm]:{100}@1.0[pleochroism:strong] + {010}@0.9 + {001}@1.2 + {110}@0.7
Related Minerals
Other minerals in the orthorhombic system
