Grown, Not Found: A Field Guide to Lab-Grown Gem Material

Some of the material on a faceter's bench came out of the ground. A lot of it came out of a furnace, an autoclave, or a plasma. This is a plain guide to the second kind: what each one actually is, whether nature bothers to make it too, and what it was invented to do before anyone thought to cut it.

Every material below is plotted by the two numbers a cutter cares about first — how hard it is, and how strongly it bends light. Color is dispersion (fire) and dot size is density. Click any one to read its page.

456789101.41.61.82.02.22.42.62.8Mohs hardness →Refractive index →Mohs 7 — airborne dust is quartz. Softer than this and everyday wear dulls itRI 2.417 — diamondGGG — Mohs 6.5–7, RI 1.970 (+0.060), dispersion 0.045, SG 7.05 GGGLuAG — Mohs 8.5, RI 1.84, dispersion ≈0.025, SG 6.73 LuAGGAGG — Mohs ≈8, RI ≈1.92, dispersion ≈0.03, SG ≈6.6 GAGGCubic zirconia — Mohs 8–8.5, RI 2.15–2.18, dispersion 0.058–0.066, SG 5.6–6.0 Cubic zirconiaZincite — Mohs 4–5, RI 2.013–2.029, dispersion 0.127, SG 5.68 ZinciteYAP (Pr:YAlO₃) — Mohs 8.5, RI ≈1.92–1.95, dispersion ≈0.02, SG 5.35 YAP (Pr:YAlO₃)Strontium titanate — Mohs 5–6, RI 2.409, dispersion 0.190, SG 5.13 Strontium titanateLithium niobate — Mohs 5–5.5, RI 2.21–2.30, dispersion 0.120, SG 4.64 Lithium niobateYAG — Mohs 8–8.5, RI 1.833 ±0.010, dispersion 0.028, SG 4.50–4.60 YAGRutile — Mohs 6–6.5, RI 2.616–2.903, dispersion 0.280, SG 4.25 RutileYVO₄ — Mohs ≈5, RI 1.99 / 2.22, dispersion ≈0.08, SG 4.22 YVO₄Corundum — Mohs 9, RI 1.762–1.770, dispersion 0.018, SG 3.99–4.00 CorundumNanosital — Mohs 7, RI 1.65–1.70, dispersion 0.015, SG 3.5–4.0 NanositalChrysoberyl — Mohs 8.5, RI 1.745–1.755, dispersion 0.015, SG 3.73 ChrysoberylSpinel (flux) — Mohs 8, RI ≈1.718, dispersion 0.020, SG 3.58–3.61 Spinel (flux)Diamond — Mohs 10, RI 2.417, dispersion 0.044, SG 3.52 DiamondMoissanite (SiC) — Mohs 9.25, RI 2.648–2.691, dispersion 0.104, SG 3.21 Moissanite (SiC)Fluorite — Mohs 4, RI 1.434, dispersion 0.007, SG 3.18 FluoriteBeryl — Mohs 7.5–8, RI 1.564–1.600, dispersion 0.014, SG 2.67–2.78 BerylQuartz — Mohs 7, RI 1.544–1.553, dispersion 0.013, SG 2.65 Quartz
Color = dispersion    0.007 → 0.280Dot size = density (2.6 → 7.1 g/cm³)Click any material

Three questions, asked of everything

The catalog names are a mess. Some describe chemistry, some are trade names, some are marketing. Rather than memorize them, it helps to ask the same three questions of any material you're handed. Every page here answers them in the same box, in the same order.

Question oneDoes nature make it too? Some of these have a common natural twin. Some have a natural equivalent so rare it has never been cut. Some have none at all — nature simply doesn't run the process. Question twoHow is it grown? Nine machines cover almost everything. The method leaves fingerprints in the stone, and it largely sets the price. Question threeWhat was it invented for? Most of this material was developed for lasers, wafers, scanners or radio sets. The gem trade is usually a downstream customer, not the reason it exists.

If you're new, read in this order

  1. Synthetic vs. simulant vs. imitation — three words that get used interchangeably and shouldn't be. Ten minutes here saves a lot of confusion later.
  2. How they're grown — the machines, drawn in cross-section.
  3. Then jump to whatever's on your bench.

The materials

Nature makes these too

CorundumAl₂O₃

Sapphire and ruby. Grown at least seven different ways, from the cheapest gem material on earth to flux crystals that fool laboratories.

Direct twinBerylBe₃Al₂Si₆O₁₈

Emerald, aquamarine, morganite, red beryl. Flux and hydrothermal, and the two look nothing alike inside.

Direct twinQuartzSiO₂

Amethyst, citrine, smoky. Grown by the thousands of metric tons for electronics; the pretty colors are a sideline.

Direct twinSpinelMgAl₂O₄

Two completely different synthetic spinels exist, and only one has the same recipe as the natural stone.

Direct twinChrysoberylBeAl₂O₄

Alexandrite. Also the single most impersonated gem in the lab-grown trade.

Direct twinDiamondC

Squeezed in a press or grown from a plasma. Two methods, two very different sets of tell-tales.

Direct twin

Nature makes them, but essentially never as gems

Cubic zirconiaZrO₂

Melted in a crucible made of itself. There is a natural equivalent, but it's rare, small and never gem material.

Rare echoMoissaniteSiC

Industry made it two years before anyone found it in nature. Still true today at any useful size.

Rare echoRutileTiO₂

More than six times the fire of diamond and enough birefringence to make the pavilion look doubled.

Rare echo

Nature never makes these

NanositalSiO₂–Al₂O₃

Not a crystal and not a glass. A block of glass grown full of crystals too small to see.

No natural analogYAG, LuAG, GGG, GAGGR₃M₅O₁₂

Garnet-structured, but no garnet nature has ever made. Doped with cerium, three of them glow absurdly.

No natural analogThe exotics shelfvarious

Lithium niobate, strontium titanate, YVO₄, YAP, zincite, fluorite, KTP and the rest.

No natural analog

Reference

TableEvery property, side by sideHardness, RI, birefringence, dispersion, density, growth method and origin for everything on this site. WorkshopAt the benchWhat each material does under the lap: heat sensitivity, cleavage, orientation, polish choices, and where people lose stones.

Grown, not found: the field guide

Nature barely does

Synthetic vs. simulant →

A reference to lab-grown gem materials, written for cutters. Values are typical published figures; ranges vary with composition, dopant and measurement wavelength. Nothing here is a substitute for a laboratory report on a stone whose identity matters commercially.