Black Star Sapphire
Corundum var. Black Star Sapphire · Precious Gemstone
Crystal System
Trigonal; typically hexagonal bipyramidal or tabular prismatic, occurring here as a cabochon cut
Mineral Group
Oxides (Hematite group)
Chemical Formula
Al2O3 (with Iron and Titanium oxide inclusions)
Formation Process
Magmatic crystallization in aluminum-rich, silica-poor environments or through regional metamorphism
About This Crystal
An opaque, brownish-black to deep black gemstone with a vitreous to sub-metallic luster. It is cut en cabochon to display its hallmark asterism.
Physical Characteristics
Color: Black; Streak: White; Cleavage: None (has parting); Fracture: Conchoidal; SG: 3.98-4.06; Fluorescence: Inert
Optical Properties
Refractive Index: 1.762-1.770; Birefringence: 0.008; Asterism (six-rayed star) caused by light reflecting off oriented hematite/rutile needles
Hardness & Durability
Origin Region
Thailand (Chanthaburi), Australia, and Africa; formed in basaltic terrains or metamorphic rocks
Hardness & Durability
Mohs Hardness: 9; Toughness: Excellent; Very stable and highly durable for everyday jewelry wear
Care & Maintenance
Clean with warm soapy water; safe for ultrasonic cleaners if no fractures are present; store separately from other gems
Rarity & Value
Relatively common compared to blue sapphire; value based on the sharpness and centering of the ‘star’ and the depth of black color
Special Characteristics
Displays 6-rayed asterism (star effect); inclusions often consist of microscopic silk-like needles of hematite or ilmenite
Lore & History
Historically known as a stone of protection; traditionally associated with the Root Chakra and believed by some to offer grounding energy