Certified origin. Untreated material. Average brilliancy of 40 to 60%. Add to 20% or deduct to 10% for other cutting. Prices for ovals and cushions. Add 8% to 10% for rounds and pears. Add 10% to 20% for emeralds and marquis.
Heat treated material. Average brilliancy of 40% to 60%. Add to 20% or deduct to 10% for other cutting. Prices for ovals and cushions. Add 8% to 10% for rounds and pears. Add 10% to 20% for emeralds and marquis. Note: If certified Burmese and untreated, add 50%, except fair or lower grades. Typically, mid-quality untreated blue sapphire will sell for 20-30% more than a treated stone of the same quality. Top-quality unheated stones could get a premium of 50% or higher, especially if they’re large.
Average brilliancy of 30% to 40%. Add to 20% or deduct to 10% for other cutting. Prices for ovals and cushions. Add 7% to 10% for rounds, pears and marquis. Add 15% to 30% for emerald cuts.
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The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
See our article called Phenomenal Gems to read more about the grading and valuation of stones with asterism.
|Is a Variety of||Sapphire|
|Colors||All except red.|
|Fracture||Conchoidal, Frequent parting|
|Luminescence||See "Identifying Characteristics" under the Sapphire main gem listing.|
|Luminescence Type||Fluorescent, UV-Long, UV-Short, X-ray Colors|
|Absorption Spectrum||See "Identifying Characteristics" under the Sapphire main gem listing.|
|Optics||RI: o = 1.757-1.770; e = 1.765-1.779 (usually 1.760, 1.768); Uniaxial (-).|
|Optic Sign||Uniaxial -|
|Luster||Vitreous to adamantine.|
|Polish Luster||Vitreous to subadamantine.|
|Specific Gravity||3.99-4.10; usually near 4.0|
|Enhancements||Heat treated: common. Diffusion treatment (places a thin blue coating on colorless sapphire): occasional. Irradiation (turns colorless gems yellow, orange, or light blue.): rare.|
|Typical Treatments||Heat Treatment, Irradiation, Lattice Diffusion|
|Transparency||Transparent to opaque.|