trigonal Synthetic synthetic corundum

Kashan Flux Ruby (Crystal)

Formula Al2O3:Cr

Crystal Structure

CDL Notation

 #! Species: Kashan Flux Ruby
#! System: Trigonal (-3m)
#! Habit: Tabular to prismatic from Pt-crucible flux growth
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 -

Physical Properties

Crystal System: trigonal
Hardness (Mohs): None
Specific Gravity: 3.99
Cleavage: None (parting on {0001} and {10-11})
Fracture: Conchoidal
Lustre: Vitreous to adamantine

Optical Properties

Refractive Index: 1.762
Birefringence: 0.008
Optical Character: Uniaxial -
Dispersion: 0.018
Pleochroism: strong: purplish-red / orangey-red
Fluorescence: Very strong red (LW and SW UV; characteristic of pure Cr3+ environment)

Origin & Identification

Origin: Synthetic
Growth Method: Flux (molybdate-based Flux In Platinum Crucible; Slow-cooling Crystallisation; Independently Developed From Chatham Process)
Manufacturer: Kashan Inc. (produced 1968-1996; associated with Inamori/Kyocera technology)
First Produced: 1968
Diagnostic Features: Angular flux fingerprints (Kashan flux residue forms angular, more geometric fingerprint textures rather than the wispy cloud-like veils of Chatham/Knischka — angular, partially solidified flux inclusions visible under dark-field illumination); platinum platelets (flat hexagonal to irregular Pt metal from Pt crucible; same as other Pt-crucible flux products; diagnostic for all flux-grown corundum); absence of twinning (Kashan rubies rarely show polysynthetic twinning lamellae typical of natural Burmese ruby); absence of rutile silk (no fine straight rutile needles as in natural Mogok ruby); molybdenum trace (Mo from flux detectable by EDXRF; natural ruby has no Mo; highly diagnostic chemical signature); strong Cr fluorescence (both LWUV and SWUV; intense red from pure Cr3+ environment; natural Burma ruby also strong, but combination with Mo trace and Pt platelets is conclusive); absorption spectrum shows strong doublet at 692/694 nm (Cr3+ R-lines); no 450 nm Fe band (natural ruby often has Fe-related absorption at 450 nm from Thai/Cambodian origin)

Characteristics

Colours

RedPinkish-red

Common Inclusions

Angular flux fingerprints (geometric; Kashan-specific)Platinum plateletsAbsence of rutile silk

Notes

Kashan flux ruby distinguishes from generic flux ruby (Chatham/Knischka/Ramaura) by angular flux fingerprint geometry (Chatham = wispy veils); from generic flux ruby.yaml in DB. Two API-verified papers: Burch 1984, Journal of Gemmology 19(1):54 (DOI 10.15506/jog.1984.19.1.54) [VERIFIED]: "Some Observations on a Kashan Synthetic Ruby" — Pt platelets and angular flux fingerprints documented. Muhlmeister et al. 1998, Gems & Gemology 34(2):80 (DOI 10.5741/gems.34.2.80) [VERIFIED]: "flux-grown rubies in general show extremely strong red fluorescence under both longwave and shortwave UV." Mo trace by EDXRF: absent in natural ruby — chemical confirmation. Production 1968-1996; Inamori (Kyocera) technology. Distinguishes from hydrothermal (no Pt, chevron zoning) and from Verneuil (curved striae, gas bubbles, no Pt).