trigonal Synthetic synthetic corundum

Hydrothermal Ruby (Crystal)

Formula Al2O3:Cr

Crystal Structure

CDL Notation

 #! Species: Hydrothermal Ruby
#! System: Trigonal (-3m)
#! Habit: Tabular to prismatic; seed plate base; chevron Cr zoning
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: Strong red (LW and SW UV; same as natural Burma ruby)

Origin & Identification

Origin: Synthetic
Growth Method: Hydrothermal (autoclave; Aqueous HF/chloride Mineraliser; Cr Dopant; Seed Plate Of Natural Or Synthetic Corundum; 400-500 Degrees C / >1 Kbar)
Manufacturer: Tairus Joint Enterprise (Novosibirsk, Russia); Biron (Perth, Australia)
First Produced: 1985
Diagnostic Features: Hexagonal seed plate — clearly visible junction between seed crystal and hydrothermal overgrowth; the seed may have different colour intensity or inclusion suite; plate is typically hexagonally oriented parallel to c-axis of corundum; chevron (herringbone) Cr zoning — Cr colour distributed in chevron-pattern waves perpendicular to growth direction; two-phase inclusions (feathers) — liquid + gas forming irregular feather patterns; differ from natural marble-hosted ruby feathers (which contain calcite or apatite daughters); nail-head spicules — short perpendicular needles with rounded heads from hydrothermal overpressure; absence of natural ruby inclusions (no rutile silk, no calcite, no apatite, no zircon, no natural negative crystals); trace element: very low Fe (<50 ppm typically; natural ruby always >100 ppm Fe); occasionally Nb trace from autoclave walls

Characteristics

Colours

RedPinkish-red

Common Inclusions

Hexagonal seed plate junctionChevron Cr colour zoningNail-head spicules (two-phase)Two-phase fluid feathers

Notes

Hydrothermal ruby from Tairus (Novosibirsk) and Biron (Perth). Two API-verified papers: Peretti et al. 1997, Journal of Gemmology 25(8):540 (DOI 10.15506/jog.1997.25.8.540) [VERIFIED]: inclusions in hydrothermal rubies from Tairus; seed plate, nail-head spicules, chevron zoning documented. Muhlmeister et al. 1998, Gems & Gemology 34(2):80 (DOI 10.5741/gems.34.2.80) [VERIFIED]: "Hydrothermal rubies can be separated from natural rubies by their low iron content and by trace amounts of niobium that are sometimes present from the autoclave walls." Distinguishes from Kashan flux ruby (Pt platelets, angular flux masses, Mo trace) and from Verneuil (curved striae, gas bubbles).