Chrysoberyl (BeAl₂O₄) is the third-hardest natural mineral (Mohs 8.5) after diamond and corundum. Its three gem varieties are iconic: alexandrite (color-change green-to-red, Cr-bearing), cymophane (chatoyant cat’s-eye), and yellow-green chrysoberyl. Russia, Sri Lanka, and Brazil supply gem material; cyclic twinning produces the distinctive “trilling” hexagonal pseudosymmetry.
Key Facts
- Mohs hardness 8.5 — third-hardest natural mineral.
- Orthorhombic; cyclic trilling twinning produces pseudo-hexagonal aggregates.
- Alexandrite variety: dramatic color change green (daylight) → red (incandescent).
- Cymophane variety: chatoyant cat’s-eye effect.
- Forms in granitic pegmatites and metamorphic mica schists.
Notable Localities
Tokovaya River (Ural Mountains, Russia) is the alexandrite type-locality. Sri Lanka and Minas Gerais (Brazil) supply cymophane and gem material.
Found at these Localities
- Ural Emerald Mines (乌拉尔祖母绿矿)
- Eastern Brazilian Pegmatite Province (巴西东部伟晶岩省)
