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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.

Brown Diamond has a specific gravity of 3.52 and a refractive index of 2.417, with a Mohs hardness of 10. It is singly refractive.

Physical & Optical Properties

RI Range2.417
SG Range3.51–3.53
SG Typical3.52
Hardness (Mohs)10
Crystal SystemCubic
Optic CharacterSR (Singly Refractive)
Dispersion0.044
Fluorescence LWVariable
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsBrown
SpeciesDiamond
VarietyFancy Brown Diamond (Champagne / Cognac)
Brown

Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.

Through the refractometer

Brown Diamond no reading — over the limit 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORead the scale from bottom to top, then look for theliquid’s own faint line near the top. SEEThe field stays dark, with one faint line near 1.81 thatdoes not move when you change stones. MEANSOver the limit — this stone’s index is above the contactliquid’s own, so the liquid is the last thing the instrumentcan still see. That faint line is your proof the instrumentis working rather than dead. It is a RESULT: it eliminatesevery species below 1.81 in one observation. A field darkwith NO line means something else has gone wrong. Computed from gems.json — edge positions are arithmetic, not drawn. RI increases upward; the field above the boundary is the dark one.

Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.

Blue DiamondDiamondPink DiamondYellow Diamond

Key Differentiators

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.

Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Brown Diamond.

Common Simulants

Treatments

Measurement Guides

How to Identify a GemstoneHow to Measure Specific GravityHow to Use a RefractometerUV Fluorescence Testing

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

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Studying for the GIA, FGA, or FEEG practical? Brown Diamond is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.

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