Laboratory-Grown Diamond

Laboratory-Grown Diamond — composition (chemistry): C;trace elements such as N,B,H,Si and Ni may be contained.

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Laboratory-Grown Diamond — structure (overall): crystalline

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Laboratory-Grown Diamond — structure (crystal system): cubic

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Laboratory-Grown Diamond — structure (crystal habit): High-pressure high-temperature synthetic diamond (HPHT synthetic diamond for short) commonly occurs as a combination of the octahedron {111} and the cube {100}, and its crystal faces often develop dendritic or step-like growth striations.

Diamond synthesized by chemical vapour deposition (CVD synthetic diamond for short) is platy, with the {100} face developed and the {111} and {110} faces undeveloped.

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Laboratory-Grown Diamond — Mohs hardness: 10

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General note

hardness only, not durability

Laboratory-Grown Diamond — cleavage: moderate

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Laboratory-Grown Diamond — density: 3.51–3.53 g/cm³

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Qualification

The clause we cite gives 3.52, with a stated tolerance of ±0.01. The range shown here is worked out from that.

Laboratory-Grown Diamond — optic character: isotropic; CVD-grown synthetic diamonds commonly show anomalous extinction.

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Laboratory-Grown Diamond — refractive index: 2.417

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Laboratory-Grown Diamond — birefringence: none

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Laboratory-Grown Diamond — pleochroism: none

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Treatment state

untreated

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Laboratory-Grown Diamond — fluorescence (long-wave UV): HPHT synthetic diamond: generally none; CVD synthetic diamond: weak, orange-yellow; weak, yellow-green; none.

GB/T 16553—2017

UV fluorescence (long-wave UV)orange-yellowweak, CVD synthetic diamondyellow-greenweak, CVD synthetic diamondDots are illustrative colours built from the colour names, not measured values

Treatment state

untreated

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Laboratory-Grown Diamond — fluorescence (short-wave UV): HPHT synthetic diamond: generally none to strong, pale yellow, orange-yellow, green-yellow, green-blue; uneven; partly phosphorescent; CVD synthetic diamond: weak, orange-yellow; weak, yellow-green; none; short wave is usually stronger than long wave.

GB/T 16553—2017

UV fluorescence (short-wave UV)generally: pale yelloworange-yellowgreen-yellowgreen-bluenone–strong, HPHT synthetic diamondorange-yellowweak, CVD synthetic diamondyellow-greenweak, CVD synthetic diamondDots are illustrative colours built from the colour names, not measured values

Treatment state

untreated

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Laboratory-Grown Diamond — spectrum (UV-visible): yellow HPHT synthetic diamond: 550 nm absorption increasing towards short wave; colourless synthetic diamond: generally visible 270 nm absorption peak.

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Laboratory-Grown Diamond — spectrum (infrared): The intrinsic peaks of synthetic diamond fall between 1 500 cm⁻¹ and 2 680 cm⁻¹; the characteristic infrared absorption bands produced by C-C bond vibration sit at 2 030 cm⁻¹, 2 160 cm⁻¹ and 2 350 cm⁻¹.

By type, HPHT-grown stones are mostly Type Ⅰb when yellow, Type Ⅱa or Ⅱa + Ⅱb when colourless, and Type Ⅱb when blue; CVD synthetic diamond is mainly Type Ⅱa, turning into Type Ⅰb when nitrogen is added during synthesis and Type Ⅱb when boron is added.

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Laboratory-Grown Diamond — spectrum (Raman): Synthetic diamond shows its characteristic Raman peak at 1 332 cm⁻¹.

As to photoluminescence (PL): HPHT synthetic diamond mostly carries luminescent peaks from Ni defects, with double peaks at 883.2 nm and 884.9 nm commonly seen at low temperature (liquid nitrogen); CVD synthetic diamond mostly carries luminescent peaks tied to [Si-V] defects, with double peaks at 737.6 nm and 737.9 nm that may be seen at low temperature (liquid nitrogen).

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Laboratory-Grown Diamond — magnification: metal inclusions visible in HPHT-grown synthetic diamond, clouds of pinpoint inclusions, colour bands or blocks that follow the growth sectors, in CVD-grown synthetic diamond, pinpoint inclusions may be present.

GB/T 16553—2017

Treatment state

untreated

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Laboratory-Grown Diamond — quality factor (lustre): adamantine

GB/T 16553—2017

Treatment state

untreated

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