Pure vibrant red to slightly purplish red; colored by trace chromium substituting for aluminum in the crystal lattice....
Chemical formula
Al₂O₃ + Cr³⁺ (Aluminum Oxide with trace Chromium)
Corundum • Corundum
Blue Sapphire
Ranging from pastel sky blue to deep velvety royal and cornflower blue, caused by intervalence charge transfer between iron (Fe2+) and titanium (Ti4+).
Al₂O₃ + Fe²⁺/Ti⁴⁺ (Aluminum Oxide with Iron and Titanium intervalence charge transfer)Mohs 9.0 Mohs
Mineralogical & Gemological Profile
| Mineral Family | Corundum |
|---|---|
| Mineral Species | Corundum |
| Gemological Variety | Blue Sapphire |
| Chemical Composition | Al₂O₃ + Fe²⁺/Ti⁴⁺ (Aluminum Oxide with Iron and Titanium intervalence charge transfer) |
| Crystal System | Trigonal |
| Mohs Hardness | 9.0 Mohs |
| Specific Gravity | 3.95 – 4.03 |
| Refractive Index | 1.762 – 1.770 |
Color Characteristics & Optical Behavior
Ranging from pastel sky blue to deep velvety royal and cornflower blue, caused by intervalence charge transfer between iron (Fe2+) and titanium (Ti4+).
Geological Context & Pakistani / Global Localities
Occurs in desilicated pegmatites, metamorphic gneisses, marbles, and secondary alluvial gem gravels across Sri Lanka, Kashmir/Himalayan terrains, Madagascar, and Myanmar.
Collector Interest & Rarity Factors
Collectors prize velvety blue sapphires exhibiting microscopic rutile silk that scatters light evenly, as well as euhedral hexagonal dipyramidal crystal specimens.
Fine Jewelry Applications
A premier gemstone for engagement rings, signet rings, cufflinks, and heirloom necklaces due to its absence of cleavage and Mohs 9 hardness.
Treatment Considerations & Disclosure
Heat treatment is standard practice to deepen blue saturation or clarify silk. Titanium or beryllium lattice diffusion also exists in the market and must be strictly disclosed.
Care & Cleaning Instructions
Clean gently with warm water, mild soap, and a soft brush. Avoid harsh thermal shock or chemical solvents if surface-reaching inclusions are present.
Traditional Meaning
Traditional Symbolism & Cultural Heritage
Traditionally associated across Persian, Greco-Roman, and South Asian cultures with wisdom, sincerity, contemplation, and fidelity. September birthstone.
Note: Cultural and birthstone traditions are presented strictly as historical folklore, never as scientifically verified medical or metaphysical effects.
Corundum
Related Entries
Delicate baby pink to vivid magenta-pink. Separated gemologically from ruby by tone and saturation thresholds defined by major...
Chemical formula
Al₂O₃ + Cr³⁺ (Aluminum Oxide with lower trace Chromium concentration than Ruby)
Pale lemon yellow to rich canary and golden amber hues.
Chemical formula
Al₂O₃ + Fe³⁺ (Aluminum Oxide with trace Ferric Iron and color centers)