Gemology Fast Track / Unit 19 of 24 · Man-made & treated · 60 min
Synthetics, simulants and assembled stones
Goal: Know the growth methods and the inclusions each one leaves.
Flame fusion (Verneuil)Powder melted through a flame onto a boule.Curved striae · gas bubbles · Plato linesCorundum, spinel, rutile, strontium titanate
Czochralski (pulling)Crystal pulled from a melt.Curved striae (faint) · bubbles · very cleanAlexandrite, corundum, YAG, GGG, forsterite
Flux growthDissolved in molten flux, crystallises slowly over months.Flux fingerprints/veils · Pt platelets · seedEmerald, ruby, alexandrite, spinel
HydrothermalHot pressurised water in an autoclave, on a seed plate.Chevron growth · nail-head spicules · bread-crumbsQuartz, emerald, ruby
Skull meltingMelt contained by its own cooler crust.Flawless; occasional bubblesCubic zirconia
HPHT / CVDDiamond growth at high pressure or from gas plasma.Metallic flux / layered strainDiamond
Assembled stones: how to catch them
Garnet-topped doublet
Red ring table-down on white paper; lustre change where garnet meets glass; bubbles below.
Opal doublet/triplet
Straight join line on side, flat black back, glassy cap.
Soudé emerald
Colourless top + bottom; green layer at girdle (immersion side view).
Sapphire doublet
Natural sapphire crown + synthetic pavilion; different inclusions top vs bottom, join plane with flattened bubbles.
Immersion trick
Drop the stone in a glass of water (or baby oil, RI ~1.47) over white paper. Side view shows join planes, colour layers, diffusion rims, curved banding far more clearly.
Red flags from sellers
Too clean for the speciesToo vivid / too cheapCalibrated identical parcels of 'natural' Type III gemsRough that looks like broken boule pieces (curved surfaces)Tumbled 'rough' with uniform colour
Gems in this unit (33)
Mystic topazImitation pearlSynthetic corundum (flame fusion)Synthetic corundum (flux / hydrothermal)Synthetic star corundumSynthetic colour-change corundumSynthetic emerald (flux)Synthetic emerald (hydrothermal)Synthetic alexandriteSynthetic spinel (flame fusion)Synthetic spinel (flux)Synthetic quartzSynthetic opalImitation opalOpal doublet / tripletImitation turquoiseSynthetic moissaniteCubic zirconiaYAGGGGStrontium titanateSynthetic rutileLab-grown diamond (HPHT)Lab-grown diamond (CVD)GlassGoldstonePlasticGarnet-topped doubletSoudé emeraldSynthetic forsteriteGlass-filled rubyHematineSynthetic turquoise
Full gem records open in the members' Gem database.
Practical
Buy one cheap flame-fusion synthetic ruby or sapphire (a few dollars). Examine in brightfield with a white diffuser to find curved striae. This single exercise trains your eye more than any reading.
Unit quiz
0/6 answered