Topaz rates an 8 on the hardness scale. It is a hard brilliant stone with a fine color range. In fact, the color of a topaz is more important than the size in determining its value. Topaz occurs naturally in a range of colors and is heat-treated to produce the more popular hues. True topaz is found in shades of colorless to yellow, orange, red or brown, and is sometimes treated by irradiation to produce blue colors. The term “imperial topaz” refers to stones with a fine peachy to reddish orange color. Today, pink, blue, and honey colored stones are the most sought after, while deep golden yellow and pink are the most valuable (natural pink stones are rare- most are heat treated yellow stones).
Blue topaz is the variety of topaz most available today. Much colorless topaz is irradiated and heat-treated to a range of blues, some of which are almost indistinguishable from aquamarine with the naked eye. What makes a blue topaz different from an aquamarine is its lack of pleochroism. Aquamarine always displays a very attractive pleochroism from blue to greenish-blue or bluish-green. Blue topaz usually has a more definite blue, perhaps with a grayish tone, which certainly distinguishes it from aquamarine.
As with all light colored gems, the value of the blue topaz increases with its intensity of color. Blue topaz has a definite sky-blue color and is uniform in color, often without overtones. While it is often pale, it can also be bright or sometimes even an intense blue. It can sometimes also have a slight gray or even greenish tinge.
Topaz is an aluminum silicate that contains up to 20% fluorine or water. Its physical and optical properties vary according to the proportions of water and fluorine present. Golden brown and pink topaz contain more water and tend to form longer crystals. Topaz is one of the hardest silicate minerals. It makes an excellent mineral specimen because of its high luster, attractive colors and well-formed crystals.
A distinctive feature of the topaz is its perfect easy cleavage. This requires careful handling when stones are cut and polished, since specimens may split or develop internal cracks.
Topaz produces some of the largest crystals. They can be up to 3 feet long and weigh up to several hundred pounds. The largest stones have been nearly 20,000 carats. One of largest topaz stones in the world sits in the Museum of Natural History in New York City. It comes from Brazil and weighs a shocking 600 lbs! The largest cut topaz, the pale blue “Brazilian Princess” found at Teofilo Otoni North of Rio De Janeiro, weighs 21,327 carats and was fashioned as a square cut. It is now on display at the Smithsonian Institution in Washington DC.
The best way to clean topaz is with warm soapy water. Never clean topaz in a home ultrasonic cleaner or a steamer. It is important that the stone be protected from any sort of exposure to rapid temperature change, acids, or heat. A topaz stone will start to lose its color if kept out in the sun or exposed to other kinds of heat. Topaz is relatively hard but can crack easily if dropped so handle your topaz with care.