orthorhombic Synthetic synthetic chrysoberyl
Hydrothermal Alexandrite (Crystal)
BeAl2O4:Cr
Crystal Structure
#! Species: Hydrothermal Alexandrite
#! System: Orthorhombic (mmm)
#! Habit: Tabular; chevron zoning from autoclave growth
orthorhombic[mmm]:{110}@1.0 + {010}@0.6 + {001}@0.3
orthorhombic
mmm
{110} {010} {001}
Quick Facts
Hardness
None
Specific Gravity
3.7
Refractive Index
1.746
Optical Character
Biaxial +
Physical Properties
Crystal Systemorthorhombic
Hardness (Mohs)None
Specific Gravity3.7
CleavageDistinct {110} in two directions
FractureConchoidal
LustreVitreous
Optical Properties
Refractive Index1.746
Birefringence0.009-0.010
Optical CharacterBiaxial +
Dispersion0.015
Pleochroismstrong: Green (daylight/fluorescent) / Red to purplish-red (incandescent)
FluorescenceWeak to moderate red (LW UV)
Origin & Identification
OriginSynthetic
Growth MethodHydrothermal (autoclave; Aqueous Mineraliser Solution; Seed Plate Of Natural Or Synthetic Chrysoberyl; Growth Over Weeks At High T/P)
ManufacturerTairus Joint Enterprise (Novosibirsk, Russia); Biron (Australia); Regency (Thailand/Australia)
First Produced1990
Diagnostic FeaturesChevron (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
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).
Natural Counterpart
The natural gem this synthetic imitates
Related Minerals
Other minerals in the orthorhombic system
