Key properties
| Chemical formula | Y3Al5O12 |
| Crystal system | Cubic |
| Mohs hardness | 8.3 |
| Toughness | Good |
| Refractive index | 1.833 |
| Optic character | Single refractive |
| Dispersion | 0.0280 |
| Specific gravity | 4.50-4.60 |
| Cleavage | None |
| Fracture | Conchoidal to uneven |
| Habit | Czochralski-pulled boules cut to any shape |
| Lustre | Vitreous to sub-adamantine; polish: Vitreous to sub-adamantine |
| UV fluorescence | Varies with dopant: colourless inert to moderate orange in LW; yellow-green stones very strong yellow with phosphorescence; chromium green strong red in LW. |
| Pleochroism | None (isotropic). |
| Cause of colour | Colourless when pure. Chromium green, manganese red, cobalt blue, titanium yellow, neodymium purple with colour-change character. |
| Typical inclusions | Almost always flawless; occasional gas bubbles; doped green material can show curved striae and red flashes in transmitted light |
| Stability | Very stable to light, heat and chemicals - one of the toughest simulants ever made. |
| Heat sensitivity | None of consequence; handles bench work well. |
| Care and cleaning | Ultrasonic and steam safe; warm soapy water always fine. |
| Availability | As a diamond simulant it died with CZ's arrival (little production after the early 1980s); doped colours still turn up in vintage jewellery, and YAG remains common in industrial/optical uses. |
| Recognition | Once heavily branded (Diamonique and dozens of 1970s names), now unfamiliar except as vintage stock. |
Varieties
YAG
| Colour | usually colourless; doped green, blue, pink, red, orange, yellow and purple versions exist |
| Transparency | transparent |
| Clarity type | Flawless by design |
| Phenomena | Some Nd-doped stones show colour change |
| Appearance | Bright, clean and diamond-ish but with clearly less fire than diamond or CZ; doped greens make a convincing demantoid show at first glance. |
| Trade names | Diamonique • Diamonair • Geminair • Linde simulated diamond • Triamond (vintage brands) |
| Misnomers | 'Synthetic diamond' and, for green material, 'synthetic demantoid' (no natural garnet shares its chemistry) |
| Typical sizes | Melee to ~10 ct vintage stones |
| Cutting styles | Round brilliant mainly; green material in emerald cuts |
| Key separations | From diamond: strong see-through (windows show through the table), SG 4.55 vs 3.52, dispersion only 0.028 (less fire than diamond), fails thermal tester, no 415 nm line. From demantoid: demantoid's RI ~1.88 is the higher reading, its SG ~3.84 the lower, and its horsetail inclusions are absent in flawless YAG; YAG also hefts heavier. From CZ: CZ much higher RI (OTL) and SG 5.8. From spessartite garnet: YAG flawless at 1.833; spessartite 1.79-1.82 with natural inclusions and Mn spectrum. |
| Sources (localities) | Historically Czochralski-grown in the USA (Linde and others); current gem production minimal. |
| Availability | Vintage/collector stock mostly. |
| Market notes | Cheap curiosities now; disclose man-made nature. |
| Care notes | Very wearable - hard and stable. |
| In short | The 1970s diamond substitute with real durability: SR 1.833, SG 4.55, hardness 8.25, low fire. See-through windows and flawless clarity distinguish it from both diamond and garnet. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.50–5.00 | $3.00 – $30.00 | vintage/collector simulant | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #160
Related materials: GGG (Gadolinium Gallium Garnet)
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