Citrine

A form of yellow quartz, heat treated citrine is popular because it is an affordable yellow gemstone. Actually, natural citrine is quite rare. Natural gems are pale (low saturation).

Basically, citrine is heat treated Amethyst. You can often see elongated parti-colored stones where one end has been heated.

The process is relatively simple. At 470 degrees C., amethyst turns light yellow. At 550 - 560 C, the material becomes dark yellow to reddish brown. Smoky quartz can turn yellow at 300 - 400 C.
Properties

• Crystal System - Hexagonal (Trigonal)
• Hardness - 7
• Specific Gravity - 2.65
• Refraction - Double
• Refractive Index - 1.54 to 1.55
• Dispersion - .013
• Birefringence - .009
• Wearability - Very Good
• Special Care - None