Image: James St. John (CC BY 2.0)
orthorhombicuncommonSilicates (Borosilicates)
Dumortierite
Al₇(BO₃)(SiO₄)₃O₃
This specimen features fibrous to massive blue-violet dumortierite crystals, often appearing as radiating aggregates, embedded within a matrix of white to clear quartz.
Dumortierite Physical Properties
Mohs Hardness
7Crystal System
orthorhombicLuster
vitreousStreak Color
whiteCleavage
poor on {100} and {110}Fracture
uneven to conchoidalSpecific Gravity
3.26Colors
blue, violet-blue, pink, brown, green, whiteTransparency
translucentType Locality
Brazil (Bahia is a famous source for blue varieties)Mineral Group
Silicates (Borosilicates)Uses
gemstone, ornamental stone, ceramic materialAssociated Minerals
quartz, kyanite, andalusite, sillimanite, muscovite, tourmalineRarity
uncommonGeological Context
Dumortierite typically forms in aluminum-rich metamorphic rocks, especially those subjected to high-temperature, low-pressure regional metamorphism, and can also be found in some pegmatites.
