Alexandrite

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Natural Alexandrite Gemstone

Refractive Index : 1.755 – 1.746 (+0.004 – 0.006)

Optical Characteristic : DR, biaxial positive

Specific Gravity : 3.73 (+0.02 – 0.02)

Formula : BeAl2O4

Crystal System : Orthorhombic

Variety/Species : Natural Alexandrite

Species/Group : Chrysoberyl

Birefringence : 0.008 – 0 .010

Dispersion : 0.015

Hardness : 8.5

Toughness : Excellent

Ultrasonic : Usually Safe

Steam : Usually Safe

UV Long : Inert to moderate red

UV Short : Inert to moderate red

Pleochroism : 3 Colors

Strength : Strong

Pleochroism Colors : Strong, green, orange and purple red

Heat : Stable

Acids : No reaction

Light : Stable

Polish Luster : Vitreous to subadamantine

Fracture : Conchoidal

Fracture Luster : Vitreous to greasy

Clarity Type : II

Tones : 2-8

Saturations : 1-3

Cause of Color : Chromium

Enhancements : None

Cleavage : None.

Color Range : Daylight: strongly bluish green, green, yellowish greenIncandescent: orangy red, red, purple-red, purplish red, red-purple Purplish, reddish, bluish, greenish

Transparency : Transparent

Phenomena : Asterism, color change, 4 ray star chatoyancy

Separations : Alexandrite from-Andalusite : RI, SG, pleochroism, spectrumColor change garnet: RI (pos) birefringence, optic character, pleochroism, spectrum, magnification.All corundum: RI, optic character, spectrum, magnification, SG.All spinel: RI, birefringence, optic character, magnification, SG.Synthetic Alexandrite: magnification, fluorescence (possibly)

Identifying Characteristics and informationUsually biaxial positive (DR B+) but may be biaxial negative (DR B-).Color change.Fingerprint inclusion, silk, include crystals, and liquid inclusions.May fluoresce a weak red (LW and SW)

Spectral DataNarrow doublet@ 6805 6975. Weak, narrow lines@ 6650, 6650, 6490 and broad band @ 6400-5550.

Trade Names and Misnomers
Alexandrite
Cat’s Eye alexandrite (S)

Tags: Alexandrite, Cat's Eye alexandrite, natural alexandrite, synthetic alexandrite