GEMSTONE SPECIES - INORGANIC

Chrysoberyl refers to the non-phenomenal varieties of the chrysoberyl mineral, which do not show a cat's eye effect or colour change (like Alexandrite). While not as rare or famous as its phenomenal counterparts, it is still a highly valued gemstone for its clarity, durability, brilliance and two famous varietiesa are Cat’s Eye Chrysoberyl and Alexandrite.
Colour Causes:
--> Yellow to green color spectrum is due to iron content.
--> Richer yellow or green hues are more valuable.
Treatment:
Most chrysoberyl is untreated. Its natural brilliance and color typically do not require enhancement. 

Chrysoberyl Cat’s Eye, also known as Cymophane, is a fascinating gemstone famous for its sharp, luminous band of light that moves across the surface, resembling the slit eye of a cat,  a phenomenon called chatoyancy.
What Causes the Cat’s Eye Effect?
--> Chatoyancy in cat’s eye chrysoberyl is caused by parallel needle-like inclusions, usually of rutile or other minerals.
--> When the gem is cut as a cabochon (smooth, dome shape), these inclusions reflect light in a single bright band across the surface.
Quality Grading Factors:
Sharpness of the Eye  --> The more defined and centered the eye, the higher the value.
Colour --> Rich, honey-toned colours are most desirable.
Transparency --> Semi-transparent to translucent stones with a strong eye are best.
Eye Movement --> A good cat’s eye appears to "open and close" as the gem is rotated.
Treatment:
Generally, untreated natural cat’s eye is prized.
Be aware of imitations made from quartz or glass. 

Alexandrite is a valuable variety of chrysoberyl known for its remarkable colour-change phenomenon. Often described as "emerald by day, ruby by night," this unique gemstone colour
Change Phenomenon:
Daylight or fluorescent light --> rs green to bluish-green
Incandescent or candlelight -->  red to purplish-red
The change is caused by complex light absorption due to trace amounts of chromium in its crystal structure, one shifts colour based on lighting conditions.
Value Factors:
Strong, dramatic colour change --> Most valued trait.
Size --> Large stones are extremely rare and highly priced.
Origin -->  Russian stones are considered the finest.
Treatment:
Typically, untreated, clarity-enhancing treatments are sometimes used.