YAG

Colorless in its undoped form; rare earth dopants produce yellow, green and pink material

Colorless Green Pink Yellow

Optical properties

Optical characteristics

Ref. index: 1.833
Luster: Adamantine to vitreous
Pleochroism: None None; singly refractive and isotropic.
Fluorescence: Undoped YAG is inert under both long- and short-wave UV. Rare earth-doped material produces characteristic emissions that vary by dopant.

Origins

Source localities

Global Lab-created: global

Commercial

Grown by the Czochralski method. Production was concentrated in the 1960s and 1970s for gem and industrial use.

100% est. supply

Identification

Instruments used

Hydrostatic Scale Measures specific gravity, works even on opaque stones 10x Loupe Your most-used instrument, start every examination here Polariscope Determines single vs. double refraction, quick and conclusive Refractometer Measures refractive index, the backbone of gem identification UV Lamp, Long Wave and Short Wave Fluorescence exposes treatments, synthetics, and origin

Specifications

Hardness: 8 Mohs
Ref. index: 1.833
Sp. gravity: 4.55 – 4.6
Crystal system: Cubic
Luster: Adamantine to vitreous
Species: Yttrium Aluminium Garnet

Market price $ 5 – 80+ / ct

No significant gem market exists for YAG today. Collector interest is limited to faceted stones from the 1960s-70s simulant era.

Rarity Very Common

Entirely synthetic. No natural analogue exists. Production peaked in the late 1960s as a diamond simulant and declined sharply after cubic zirconia became commercially available around 1976.

Confused with

Diamond YAG lacks diamond's fire. Dispersion of 0.028 versus diamond's 0.044 means noticeably less coloured flash. RI and SG are both well below diamond.
Cubic Zirconia Both are isotropic synthetics used as diamond simulants, but CZ has higher RI (2.15-2.18) and stronger dispersion. A refractometer reading separates them immediately.
Synthetic Spinel Synthetic spinel is also isotropic but has lower RI (1.728) and lower SG (3.63). Refractometer and hydrostatic scale distinguish the two.

Expert tip

YAG reads off the scale on a standard refractometer. Confirm isotropy with the polariscope, then use SG (4.55-4.60) as the primary separating measurement.