orthorhombic Synthetic synthetic chrysoberyl

Hydrothermal Alexandrite (Crystal)

Formula BeAl2O4:Cr

Crystal Structure

CDL Notation

 #! Species: Hydrothermal Alexandrite
#! System: Orthorhombic (mmm)
#! Habit: Tabular; chevron zoning from autoclave growth
orthorhombic[mmm]:{110}@1.0 + {010}@0.6 + {001}@0.3

Crystal System orthorhombic

Point Group mmm

Crystal Forms (3)

{110} {010} {001}

Quick Facts

Hardness

None

Specific Gravity

3.7

Refractive Index

1.746

Optical Character

Biaxial +

Physical Properties

Crystal System: orthorhombic
Hardness (Mohs): None
Specific Gravity: 3.7
Cleavage: Distinct {110} in two directions
Fracture: Conchoidal
Lustre: Vitreous

Optical Properties

Refractive Index: 1.746
Birefringence: 0.009-0.010
Optical Character: Biaxial +
Dispersion: 0.015
Pleochroism: strong: Green (daylight/fluorescent) / Red to purplish-red (incandescent)
Fluorescence: Weak to moderate red (LW UV)

Origin & Identification

Origin: Synthetic
Growth Method: Hydrothermal (autoclave; Aqueous Mineraliser Solution; Seed Plate Of Natural Or Synthetic Chrysoberyl; Growth Over Weeks At High T/P)
Manufacturer: Tairus Joint Enterprise (Novosibirsk, Russia); Biron (Australia); Regency (Thailand/Australia)
First Produced: 1990
Diagnostic Features: Chevron (herringbone) zoning — most characteristic growth feature; Cr colour zoning follows chevron growth fronts of autoclave-grown crystal in a V-pattern parallel to seed plate; visible under microscope with diffuse lighting; seed plate — visible (or implied by growth geometry) junction between seed and overgrown material; nail-head spicules — short nail-head-shaped two-phase inclusions (liquid + gas) oriented perpendicular to growth layers; characteristic of hydrothermal growth under high pressure; absence of flux inclusions (no Pt platelets; no flux veils — distinguishes from flux-grown); wavy growth planes (hydrothermal growth planes visible as wavy parallel lines under immersion); EDXRF: high purity; absence of Fe distinguishes from natural and Czochralski

Characteristics

Colours

Green (daylight)Red to purplish-red (incandescent)

Common Inclusions

Chevron growth zoning (Cr colour)Seed plate junctionNail-head spicules (two-phase)

Notes

Hydrothermal alexandrite from Tairus (Novosibirsk), Biron (Australia), and Regency. Peretti, Mullis, Mouawad & Guggenheim 1997, Journal of Gemmology 25(8):540 (DOI 10.15506/jog.1997.25.8.540) [VERIFIED]: inclusions in hydrothermal rubies and sapphires from Tairus (Novosibirsk); diagnostic suite applies by analogy to hydrothermal alexandrite from same manufacturer. Russian flux-grown alexandrite diagnostics confirmed by Schmetzer et al. 1996 (DOI 10.5741/gems.32.3.186) [VERIFIED] for comparison. Three-way distinction: Czochralski (curved striae + iridium inclusions); flux (Pt platelets + flux veils); hydrothermal (chevron zoning + nail-head spicules + seed plate).