Citrine, yellow to red-orange quartz, was once the Rodney Dangerfield of the gem world; its sheer abundance being responsible for this "no respect" treatment. That has begun to turn around somewhat in the last couple of decades as fashions have repeatedly emphasized earth tones and home shopping networks have marketed the various shades of citrine aggressively with catchy adjectives like "butterscotch" and "whiskey".
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Quartz|
|Refractive Index||1.544 - 1.553|
|Wearability||* Very Good|
|Enhancements||Amethyst can be heat treated to change it to citrine. Not common. "Madeira" Citrine" with red flashes is a result of heat treatment.|
Citrine, yellow to red-orange quartz, was once the Rodney Dangerfield of the gem world; its sheer abundance being responsible for this “no respect” treatment. That has begun to turn around somewhat in the last couple of decades as fashions have repeatedly emphasized earth tones and home shopping networks have marketed the various shades of citrine aggressively with catchy adjectives like “butterscotch” and “whiskey”.
Actually, very little of the quartz which is mined is citrine. Natural stones tend to be pale yellow, often with smoky tones. The vast majority of citrine which is marketed is produced by heating smoky quartz, (which produces light to medium yellows,) and amethyst, (which produces stronger yellows and orange-red to orangey brown shades.) The treatment is usually done right at the mine, and is stable, and fully accepted within the gem trade. Recently, colorless quartz from some mines have been irradiated and heated to produce a neon, slightly greenish yellow, usually called Lemon Quartz. … In the past, it was commonplace for citrine to be given misnomers such as, “Brazilian topaz”, “Madeira topaz,” etc. The higher gemological knowledge level of both jewelers and the public make this practice rare today. This gem is a fine jewelry stone, with no cleavage and a hardness of 7. Furthermore, its availability in large sizes enables cutters to use it for dramatic and intricate custom cuts. It is also used for gem carvings. Stable in light and not very sensitive to chemicals, this stone requires no special care and can be used for any jewelry application. Virtually all citrine comes from Brazil.
At the top end of the scale are prime specimens of the most saturated yellows, oranges and reddish tones. Those with less intense color fall into lower value ranges with pale or smoky stones at the bottom. As with any gem material custom cutting increases value and inclusions decrease it. There is no exponential increase in value per carat with increase in size as larger sizes are readily available. In many fancy cut or carved specimens, the majority of the value is due to the artistry of the fashioning.
Source/Attribution: Barbara Smigel at Artistic Colored Stones