trigonal Synthetic synthetic corundum

Czochralski Sapphire (Crystal)

Al2O3

Crystal Structure

CDL Notation

 #! Species: Czochralski Sapphire
#! System: Trigonal (-3m)
#! Habit: Cylindrical boule with prismatic habit
trigonal[-3m]:{10-10}@1.0 + {10-11}@0.8 + {0001}@0.5

Crystal System trigonal

Point Group -3m

Crystal Forms (3)

{10-10} {10-11} {0001}

Quick Facts

Hardness

None

Specific Gravity

3.99

Refractive Index

1.762

Optical Character

Uniaxial -

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Physical Properties

Crystal Systemtrigonal

Hardness (Mohs)None

Specific Gravity3.99

CleavageNone (parting on {0001} and {10-11})

FractureConchoidal

LustreVitreous to adamantine

Optical Properties

Refractive Index1.762

Birefringence0.008

Optical CharacterUniaxial -

Dispersion0.018

Pleochroismweak: Blue / Pale blue to colourless

FluorescenceWeak to inert (Linde blue may show weak orange-red under SWUV)

Origin & Identification

OriginSynthetic

Growth MethodCzochralski (melt Pulling; Seed Rod Pulled Upward From Melt Surface Under Rotation)

ManufacturerLinde Division (Union Carbide, USA); Kyocera Corp. (Japan); Crystal Systems Inc.; Rubicon Technology; Saint-Gobain

First Produced1958

Diagnostic FeaturesTight curved growth striae (finer and more closely spaced than Verneuil; concentric arcs around growth axis under immersion); absence of gas-bubble trains (characteristic of Verneuil but absent in Czochralski); absence of curved colour banding; platinum-group metal (PGM) rod-like inclusions from seed holder (highly diagnostic of Linde boules); no natural inclusion suite (no rutile silk, no zircon, no negative crystals); Linde star sapphire: artificially precipitated rutile needles (too perfect and uniformly spaced under magnification; typically on flat-back synthetic dome)

Colours

BlueColourlessVarious (by doping)

Common Inclusions

Tight curved growth striaePlatinum-group metal rod inclusions (PGM from seed holder)Absence of natural inclusions (no rutile silk)

Notes

Czochralski sapphire grown from melt pulled upward on rotating seed rod; produces a boule rather than Verneuil pear-shaped boule. Key distinction from Verneuil: tighter curved striae (vs broader curves in Verneuil); no gas-bubble trains; PGM inclusions from seed holder. EDXRF/LA-ICP-MS: extremely low trace elements (Ga typically below detection in natural sapphire >1 ppm). Linde star ruby/sapphire: Ti-doped then annealed to precipitate rutile. Gemmological properties and growth method from Read 7th ed. pp.193-195 (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED]. No dedicated peer-reviewed gemmological paper for Czochralski sapphire identification retrieved via API.