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Yellow Diamond

Last updated: April 2026

Yellow diamonds are Type Ia (Cape series, nitrogen in B-aggregates — most common natural fancy yellow) or the rarer Type Ib (isolated nitrogen, canary yellow, common in HPHT synthetics). Cape series stones show characteristic absorption at 415 nm (N3 center) and strong blue LW fluorescence.

Yellow 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 SWVariable
Chelsea FilterInert
PleochroismNone
ColorsYellow Orange
SpeciesDiamond
VarietyFancy Yellow Diamond
Yellow Orange

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

Yellow 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.

Through the polariscope

Yellow Diamond Dark throughout (SR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Yellow Diamond stays dark through the whole rotation. That is singly refractive: there is no second ray to rotate the plane of vibration back into the analyser. Computed from optic character and transparency in gems.json. A polariscope separates singly refractive, doubly refractive and aggregate — it does not show the optic sign.

Drawn from the optic character and transparency above. A polariscope separates singly refractive, doubly refractive and aggregate; the optic sign needs a conoscope. How to take this reading.

Specific gravity, and what it rules out

Yellow Diamond SG 3.51–3.53 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 8 other species in the table overlap this range, so a reading here narrows the field to 9 rather than naming the stone. Combine it with a refractive index to separate what is left. Computed from the specific-gravity range in gems.json. Hydrostatic weighing — the bench method this site recommends; heavy liquids are toxic and regulated. Faint ticks are the other species in the table.

Drawn from the specific-gravity range above, against every other species in the table. How to take this reading.

Through the dichroscope

Yellow Diamond One colour (no pleochroism) IDENTICAL AT EVERY ANGLE Yellow Diamond shows no pleochroism, so both windows match at every orientation — turning the instrument changes nothing. That is a real negative result, and the reason it is worth knowing is below. Computed from pleochroism and pleochroic colours in gems.json. Window tints are derived mechanically from the colour words, not chosen; a neutral pair depicts no colour at all.

Drawn from the pleochroism above. Two windows that match mean either no pleochroism or the wrong angle — turn the instrument to tell. How the dichroscope compares.

Blue DiamondBrown DiamondDiamondPink Diamond

Key Differentiators

Natural vs. Synthetic

Synthetic yellow diamond is commercially available (HPHT (High Pressure High Temperature) — nitrogen deliberately incorporated for Type Ib yellow; Sumitomo, New Diamond Technology, De Beers, CVD (Chemical Vapor Deposition) followed by irradiation/annealing to produce yellow color). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

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

Common Simulants

Treatments

Measurement Guides

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

Identifying a yellow 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? Yellow 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.

Practice exams →