Black Star Sapphire
Corundum var. Star Sapphire · Precious Gemstone
Crystal System
Trigonal; specifically hexagonal scalenohedral. The habit in these specimens is typically barrel-shaped or bipyramidal, but common for star-stones to be polished into a cabochon to reveal asterism.
Mineral Group
Oxides; Hematite group (Corundum species)
Chemical Formula
Al2O3 (Aluminum Oxide) with Fe (Iron) and Ti (Titanium) inclusions (Rutile/Ilmenite needles)
Formation Process
Metamorphic or Igneous. Formed in aluminum-rich, silica-poor environments. Often found in basalt-hosted deposits or secondary alluvial deposits.
About This Crystal
A dark, opaque to translucent gemstone, appearing black or dark brownish-green. It displays a silky to vitreous luster and is notable for a distinct white or gold star emanating from the center when under direct light.
Physical Characteristics
Color: Black, dark gray, or bronze-brown; Streak: White; Transparency: Opaque to semi-translucent; Cleavage: None (has rhombohedral parting); Fracture: Conchoidal to uneven; Specific Gravity: 3.95 - 4.10; Fluorescence: None to weak dark red.
Optical Properties
Refractive Index: 1.760 - 1.778; Birefringence: 0.008; Asterism: A six-rayed star caused by light reflecting off microscopic needle-like inclusions oriented in three directions; Doubly refractive.
Hardness & Durability
Origin Region
Primarily Chanthaburi and Kanchanaburi, Thailand; also found in Australia, Sri Lanka, and Africa (Madagascar).
Hardness & Durability
Mohs hardness: 9 (Second only to diamond). Extremely tough and excellent for daily jewelry wear, though parting planes can be a vulnerability.
Care & Maintenance
Safe to clean with warm soapy water or ultrasonic cleaners. Generally stable against chemicals, but avoid harsh acids. Store separately from softer stones like quartz or opal to prevent scratching them.
Rarity & Value
Relatively common compared to blue star sapphires. Value is determined by the sharpness of the star ('legs'), the symmetry of the rays, and the body color. Most black star sapphires are natural and untreated.
Special Characteristics
Asterism: The star effect is the most prominent feature. In Thai specimens, the star is often golden due to hematite/ilmenite needles, whereas Sri Lankan stones exhibit white stars from rutile.
Lore & History
Historically, star stones were carried as protective amulets for travelers. In modern crystal lore, Black Star Sapphire is associated with the Root Chakra and is believed to provide grounding, protection, and mental clarity.