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Alexandrite


Properties
Chemical Composition: 
Beryllium Aluminium Oxide - BeAl2O4
Classification / Type: 
-
Colors / Varieties: 
  • Alexandrite (color change in lamplight and daylight)
  • Alexandrite Cat's Eye
Crystal System / Forms: 
Orthorhombic System
Hardness: 
8.5
Specific Gravity: 
3.71 - 3.75
Cleavage / Fracture: 
Imperfect / Conchoidal fractur
Optic Character: 
Anisotropic, D.R.; Biaxial positive.
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.746 - 1.755 / 0.009; Range: 1.740 - 1.760
Pleochroism: 
Alexandrite exhibits strong trichroism (red, orange, green) while other varieties exhibit weak to moderate effect.
Dispersion: 
0.015
Magnification: 
Phase and fingerprints, crystalline inclusions, growth zoning - trilling boundaries.
U.V. Fluorescence: 
Inert
Spectrum: 
  • Broad absorption in the yellow-green region at 575nm and in the violet, and narrow lines in the red at 680nm and 678nm, weak lines at 665nm, 655nm, 649nm and in blue portion at around 470nm.
Cause of Color: 
Chromium
Treatment (Enhancement): 
Lighter yellow, included cat's eye irradiated to a more transparent deep brown color. Most of these were found to be radioactive.
Specific Tests & Remarks: 
Alexandrite Color
  • Green (greenish blue, bluish green, brownish green) in daylight and red (purplish red, brownish red, grayish red) in incandescent light.
  • This is due to small scale replacement of Aluminium Oxide by Chromic Oxide.
  • The transmission of the red part of the spectrum is more or less balanced and any change in the nature of the incident light will either emphasize the red or the green-blue.
  • Daylight is rich in blue wavelength while incandescent light (other than mercury vapor fluorescent lamps) is richer in red wavelengths and hence the stone exhibits the green to red color change.
Synthesis: 
Czochralski and Flux fusion method.
  • Synthetic Alexandrite
  • Synthetic Alexandrite Cat's Eye
Simulants (with key separation tests): 
  • Natural / Synthetic Color Changing Sapphire (optic figure, R.I., S.G., inclusions), Color Changing Garnet (optic character, spectrum), Tourmaline (optic figure, R.I., S.G.), Andalusite (R.I., S.G., pleochroism), Epidote (birefringence, spectrum), Natural / Synthetic Color Changing Spinel (optic character, pleochroism)
Geological Occurrence: 
In pegmatite, schist, marbles and alluvial deposits.
Sources: 
Russia, Tanzania, Sri Lanka, Brazil, Zimbabwe, India (Orissa, Tamil Nadu, Andhra Pradesh), Myanmar (Burma), Madagascar.
Cuts & Uses: 
Facetted cuts, cabochon, generally mixed cuts, also as beads, carvings, etc.

Click on this link for meaning of alexandrite gemstone.

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In Germany, the garland of ambers is hung around the necks of the infants, so that their teeth might come out without much trouble.

In Turkey, people fix a piece of amber in the hubble-bubble, dogged by an age old belief that the presence of the jewel would destroy all the germs and no disease would spread, even after many have dragged their puffs from it.

In Greece, people think if wine is poured into the cups made of amethyst, one does not get drunk after drinking that.

In Rome, a talisman having coral pieces is considered very auspicious to quell the bad spells of evil look. The Romans were in the habit of hanging chains made of ancient coral pieces from the cradle of the infants to protect them from evil effects.

In China, people wear rings studded with tiny conch or oyster shells as they believe it cures all aches such as stomach ache, worms and like.

In India, pendants made of silver and studded with pearls are hung from the necks of the children to save them from any bad effects.

Greeks still believe, if women wear blue sapphires then no sense of immorality would pollute their mind nor can any fear of the supernatural can trouble them.

The Pope Innocent III had circulated an order asking all the priests wear blue sapphire, so that morality can be strengthened.

It is said about turquoise, that when the stone changes its color into yellow, it actually signals bad times to the person who wears it.

It is believed that a turquoise gifted to a friend or a lover turns his or her life into one of happiness and good luck.

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