Chrysoberyl is a rare and durable gemstone material that chemically consists of beryllium aluminium oxide (BeAl₂O₄). Despite its name, it is not related to beryl (such as emerald or aquamarine). Chrysoberyl has a high hardness (8.5 on the Mohs scale), excellent clarity and a characteristic lustre, making it highly favoured in the world of jewellery.Chrysoberyl is a versatile and undervalued gemstone ranging from subtle yellow-green to spectacularly colour-changing alexandrite. Thanks to its hardness and natural beauty, it is an excellent choice for high-quality jewellery without requiring many treatments.

There are three main varieties of chrysoberyl:

1. Ordinary chrysoberyl
   • Usually yellow-green to brownish-green.
   • Transparent with a vitreous lustre.
   • Sometimes simply referred to as “chrysoberyl”.
2. Cat's eye chrysoberyl
   • Exhibits a sharp, silver-white band of light resembling a feline pupil (chatoyancy).
   • Usually yellow to yellow-green in colour.
   • Only stones with strong chatoyancy may officially be designated as "Cat's Eye" without further specification.
3. Alexandrite
   • Rarest form of chrysoberyl.
   • Changes colour depending on the light: green/blue-green in daylight, reddish under incandescent light.
   • Extremely sought after and precious.

Important deposits include:

1. Brazil – producer of alexandrite and ordinary chrysoberyl.
2. Sri Lanka (Ceylon) – famous for high-quality cat’s eye chrysoberyl.
3. Madagascar, Tanzania, India and Myanmar – also supply various chrysoberyl varieties.

Chrysoberyl is rarely treated compared to other gemstones. Most specimens are natural and unaltered. Possible (but rare) treatments:

1. Heating – Sometimes applied to improve colour in cat’s eye, but this is not common practice.
2. Synthetic alexandrite – Produced for jewellery, but is distinctly different under laboratory testing.

The value of chrysoberyl depends heavily on colour, clarity, rarity and origin.

1. High-quality natural alexandrite with a distinct colour change is the most valuable. A colour change from green to ruby red is particularly rare and sought after. Combined with the cat's eye phenomenon, a colour-changing alexandrite becomes even rarer and more valuable.
2. Cat's eye chrysoberyl with a sharp, bright line and a milky silk lustre. Particularly sought after in the Indian market due to spiritual significance.
3. Transparent, intense yellow-green chrysoberyl is also valued, especially in large carat weights.
4. Vanadium chrysoberyl - bright blue-green - is one of the most sought-after gemstones in contemporary fashion.