Brown Diamond
Last updated: April 2026
Brown diamonds are the most abundant fancy color. Brown color arises from plastic deformation creating vacancy clusters and graining planes. HPHT treatment routinely converts brown diamonds to near-colorless or other fancy colors. The Argyle mine used an internal scale of Champagne (C1–C5) and Cognac (C6–C7) to grade this material.
Physical & Optical Properties
Related: Diamond Varieties
Key Differentiators
- Most common fancy color — approximately 80% of all diamonds are brown or near-colorless
- Argyle mine grading: Champagne C1–C5, Cognac C6–C7
- Color from plastic deformation (more severe than pink); vacancy clusters contribute
- Extremely HPHT-treatment-susceptible — most colorless HPHT-treated diamonds were originally brown
- Thermal conductivity — passes diamond tester; RI 2.417
Natural vs. Synthetic
Synthetic brown diamond is commercially available (HPHT synthesis (brown is an intermediate or transitional color in HPHT process; deliberate brown synthesis is uncommon as HPHT typically targets colorless or yellow), CVD synthesis (as-grown CVD diamonds are often brown; require post-growth HPHT treatment to achieve colorless)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.
- DiamondView (UV fluorescence imaging): Natural brown diamonds show broad irregular blue or blue-green fluorescence patterns reflecting natural octahedral growth. Graining-related strain visible in pattern. Synthetic: HPHT synthetic shows cuboctahedral sector geometry. As-grown CVD shows columnar layered pattern with orange sectors. CVD brown (pre-HPHT) shows characteristic banded pattern.
- Spectroscopy (FTIR): Natural brown diamonds often show Type Ia nitrogen (B-aggregates, N3 center). Some show 3107cm-1 hydrogen absorption. Nitrogen aggregate pattern reflects geological thermal history. Synthetic: HPHT synthetics typically Type IIa or Type Ib (isolated nitrogen). As-grown CVD diamonds often show nitrogen-related bands inconsistent with natural geological aggregation. Si-V at 737nm (CVD).
- Loupe — graining and inclusions: Brown graining lines (parallel deformation planes) visible under magnification. No metallic inclusions. Synthetic: HPHT: metallic flux inclusions (Fe/Ni/Co), magnetically attracted. CVD: columnar growth patterns, graphite inclusions in planar arrangement. No graining planes from natural plastic deformation.
GemID Pro includes a two-phase natural vs. synthetic testing protocol for Brown Diamond.
Start Free TrialCommon Simulants
- Smoky Quartz: DR (uniaxial positive); RI 1.544–1.553; SG 2.65; hardness 7; much lower RI and SG; fails diamond thermal tester; conchoidal fracture visible.
- Brown Topaz: DR (biaxial positive); RI 1.629–1.637; SG 3.53; hardness 8; perfect basal cleavage {001}; fails diamond thermal tester.
- Brown Zircon: DR (uniaxial positive); RI 1.925–1.984 (high type); SG 4.69; hardness 7.5; strong facet doubling visible under loupe; fails diamond thermal tester.
- Hessonite Garnet: SR but RI 1.742–1.748; SG 3.65; hardness 6.5–7.5; heat shimmer inclusions (treacly texture); fails diamond thermal tester.
- Chocolate Tourmaline (Brown Dravite): DR (uniaxial negative); RI 1.624–1.644; SG 3.06; strong pleochroism; hardness 7–7.5; fails diamond thermal tester.
- Brown Cubic Zirconia: SR; RI ~2.15 (lower than diamond); SG 5.60–5.90 (much heavier); hardness 8–8.5; fails diamond thermal tester.
Treatments
- HPHT Treatment (decolorization or color change)
- Irradiation (+ annealing)
- Surface Coating
Price Context
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a brown diamond? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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