Gem of the Month

Each month this section will feature either a topic of interest to gem lovers or one special gemstone with background on the material and its value.

Go to: Homepage -- what's new in faceted gems -- what's new in designer cabochons and gem carvings -- gem of the month -- gem of the month archive -- birthstone of the month -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- about the ACS cutters -- settings for these gems --faceting information -- purchase UltraTec equipment

 

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September, 2001

PRECIOUS TOPAZ

In using the term "precious topaz", I'm referring to stones of a rich yellow to a medium peachy orange color. I've already written on blue topaz (see Gem of Month for June, 1999). In the future I'll cover Imperial Topaz which, to my way of thinking, is in a separate category of only those stones with very saturated reddish orange color. There will also be a later section on other topazes, such as pinks, browns and colorless stones. The term "precious" topaz was originally used to distinguish yellow and orangey topaz from other gems such as some citrines and smoky quartzes which had erroneously been referred to in the past as "Maderia topaz' and "smokey topaz". The confusion derives from the Brazilian word "topazio" which means yellow and was used generically by miners. Most precious topaz still comes from Brazil. Topaz of any type is a good jewelry stone and it is historically one of the most important gemstones. With its relatively high refractive index and hardness of 8, with no special sensitivity to chemicals it can be used, with appropriate care, in any jewelry application. Although perfect cleavage does present a caution, this is mostly solved in the cutting stage --cutters generally orient the table of the stone 5 -10% off the cleavage plane which results in a pretty stable stone during cutting and wearing. All that is necessary is to protect the gem from hard knocks and to avoid steamers and ultrasonics in cleaning. The subject of enhancement in the topaz family is a complicated one, but for the most part, except for colorless stones, it is prudent to assume that some form of heat and/or irradiation has been used on stones prior to cutting. The color of precious topaz is generally heat and light stable; unlike some natural and enhanced types of brown topaz which can fade dramatically in strong light. In my opinion, when you have a stone that has that good precious topaz color, there is no chance that it will be mistaken for a citrine, a yellow sapphire or any other gem-- the color is so distinctive!
Value

The hue and saturation of color is the primary determiner of value in this variety, in general the more pink or red mixed in with the yellow or orange the higher the value. Most precious topaz is native cut in Brazil, so custom cuts are strong value enhancers. Size comes at a premium in all the topazes except blue and colorless. There's an exponential jump in value in stones larger than 5 carats and again for stones larger than 10 carats.
Gemological Properties:

Makeup: Aluminum fluorohydroxysilicate

Crystal Structure: Orthorhombic

Hardness: 8

Luster: vitreous

Density: 3.54

RI: about 1.62-1.63

DR: 0.010

Dispersion: 0.014

Cleavage: Perfect in one direction
Stones Currently Available:

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Go to: Homepage -- what's new in faceted gems -- what's new in designer cabochons and gem carvings -- gem of the month -- gem of the month archive -- birthstone of the month -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- about the ACS cutters -- settings for these gems --faceting information -- purchase UltraTec equipment