Alexandrite

Alexandrite is one of the rarest and most valuable gemstones. It was discovered by chance during a search for emeralds near Yekaterinburg in 1833, on the day of Alexander the Second's birthday anniversary (hence the name).^[1] It is a very valuable variety of chrysoberyl, which ranks as the third-hardest gemstone, right after diamond and corundum.

Alexandrite changes its color depending upon the nature of ambient lighting. It is emerald-colored or grass-green in daylight and purple-reddish in artifical light. Its color varies also from red to orange-yellowish depending on the angle from which it is looked at.

Alexandrite

Basic properties

Composition	Al₂BeO₄
Class	Oxydes and hydroxydes
Crystal system	Rhombic
Mohs' hardness	8,5
Fracture	Conchoidal
Cleavage	Imperfect
Lustre	Glassy
Streak	White
Localities	Tanzania, Brazil, Sri Lanka, Republic of South Africa, India, Zimbabwe, Tasmania

References

↑ Minerały i kamienie szlachetne by RBA Collecionables, S.A., ISBN 978-83-7813-150-2, 2012.

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[1] Minerały i kamienie szlachetne by RBA Collecionables, S.A., ISBN 978-83-7813-150-2, 2012.