Ca2Al3(SiO4)3(OH)Orthorhombic
Tanzanite
Ca2Al3(SiO4)3(OH)
SilicatesChemical FormulaCa2Al3(SiO4)3(OH)
Crystal SystemOrthorhombic
Mohs Hardness6.5
Specific Gravity3.35
ColorBlue, violet, burgundy
LusterVitreous
StreakWhite
CleavageOne direction
FractureConchoidal to uneven
Occurrence
Variety of zoisite. Found only in Tanzania. Heated to enhance blue color.