Sapphire
Corundum var. Sapphire · Precious Gemstone
Crystal System
Trigonal; typically hexangular barrel-shaped, rhombohedral crystals, or tabular plates
Mineral Group
Oxides (Hematite group)
Chemical Formula
Al2O3 (with Fe, Ti impurities)
Formation Process
Metamorphic (regional or contact) and Igneous (silica-poor rocks like syenites and pegmatites), often found in alluvial deposits
About This Crystal
The specimen shows a deep blue color with visible rhombohedral or basal growth striations on the faces. It has a vitreous luster and appears translucent to opaque in this specific rough form, with some iron-rich matrix/oxidation on the right side.
Physical Characteristics
Color: Blue; Streak: White; Cleavage: None (has basal/rhombohedral parting); Fracture: Conchoidal to uneven; Specific Gravity: 3.98-4.06; Fluorescence: Generally inert to moderate (orange-red in some types).
Optical Properties
Uniaxial negative; Refractive Index: 1.762-1.778; Birefringence: 0.008; Pleochroism: Strong (violet-blue to greenish-blue); Double Refraction.
Hardness & Durability
Origin Region
Kashmir (India), Sri Lanka, Madagascar, Myanmar (Burma), Australia, and Montana (USA)
Hardness & Durability
Mohs Hardness: 9 (second only to diamond); Toughness: Excellent; Very stable and suitable for all types of jewelry.
Care & Maintenance
Clean with warm soapy water; ultrasonic and steam cleaners are usually safe for untreated stones. Store separately to avoid scratching softer gems.
Rarity & Value
High; Value is determined by 'The 4 Cs'—Color, Clarity, Cut, and Carat weight. Unheated natural blue specimens are very rare and highly valuable.
Special Characteristics
Visible growth lines (striations) on the faces. May exhibit asterism (star effect) if rutile silk is present, or color-changing properties in rare varieties.
Lore & History
Statistically the most popular colored gemstone. Historically associated with royalty, wisdom, and divine favor. Used by ancient Greeks at Delphi and by medieval clergy to symbolize heaven.