Blue Diamond

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Physical & Optical Properties

RI Range2.417

SG Range3.50–3.53

SG Typical3.52

Hardness (Mohs)10

Crystal SystemCubic

Optic CharacterSR (Singly Refractive)

Dispersion0.044

Fluorescence LWInert

Fluorescence SWStrong orange

Chelsea FilterInert

PleochroismNone

ColorsBlue Violet

SpeciesDiamond

VarietyFancy Blue

Key Differentiators

Strong blue phosphorescence after SW UV (5–30+ seconds)
Inert under LW UV (unlike Type Ia)
No 415nm Cape line on spectroscope
Boron semiconductor — may read slightly lower on thermal tester
RI > 2.40 (OTL), no facet doubling

Natural vs. Synthetic

Synthetic blue diamond is commercially available (HPHT (boron-doped), CVD (boron-doped)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

SW UV Phosphorescence Pattern: Strong blue phosphorescence lasting 5–30+ seconds. Natural IIb typically shows longer sustained glow. Synthetic: Synthetic IIb (HPHT/CVD boron-doped) may also phosphoresce with similar color. Duration, intensity, and growth pattern differ — lab confirmation (DiamondView, FTIR) required for high-value stones.

GemID Pro includes a two-phase natural vs. synthetic testing protocol for Blue Diamond.

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Common Simulants

Blue sapphire: Doubly refractive uniaxial negative; RI 1.762–1.778; SG 4.00; strong trichroism.
Aquamarine: Doubly refractive uniaxial negative; RI 1.577–1.583; SG only 2.72; much softer (7.5–8 Mohs).
Blue spinel: Isotropic SR; RI ~1.718; no trichroism; SG ~3.60.
Tanzanite: Biaxial positive DR; very strong trichroism (blue-violet-purple); lower SG (3.35); softer (6.5 Mohs).
Iolite: Biaxial negative DR; pronounced trichroism (blue-gray-pale yellow); low SG (2.58–2.66); RI 1.542–1.551.

Commonly Confused With

Commonly confused with: Sapphire, Aquamarine, Spinel, Tanzanite, Iolite.

Treatments

HPHT Color Treatment
Irradiation (blue color)

Price Context

Natural — low ($/ct)$50,000

Natural — high ($/ct)$3,000,000

NotePer carat; among the rarest gems. Fancy blue: $50k–$200k/ct; vivid fancy blue: $1M–$3M+/ct. GIA grading report with origin and type classification essential.

Synthetic — low ($/ct)$800

Synthetic — high ($/ct)$5,000

Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.

About Blue Diamond

Blue color in Type IIb diamonds is caused by trace boron. Natural Type IIb diamonds are extremely rare; most blue diamonds in commerce are color-treated or synthetic. All standard diamond ID properties apply (RI > 2.40, SR, hardness 10, adamantine luster); SW UV phosphorescence is the key field differentiator from other blue stones.

Identifying a blue diamond? GemID walks through these tests in order — RI, SG, fluorescence, and more.

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