Home >> Hobbies >> Gemology

Blue Topaz Characteristics

The word "topaz" comes from the Sanskrit for "fire"; ancient Egyptians believed its natural golden hues came from the sun god Ra. The most common color for topaz is brown, but colorless specimens also exist. Other colors include yellow, orange, red or pink, and blue. Because of its rarity, blue topaz has been revered as more mystical -- as a stone of healing and truth. Blue topaz is the birthstone for the month of December and an anniversary stone for couples celebrating the fourth year of marriage.

Color
- Natural blue topaz is rare and in short supply. Typically, the stunning color occurs courtesy of manmade techniques, such as heating treatment and irradiation; the latter enhances a colorless stone to a pale or medium-blue color due to neutron bombardment. Stones so treated can retain a certain level of radioactivity, especially if this process was used for a longer period of time for a deeper, richer color. The process is completed at a nuclear reactor, though an accelerator can yield similar results. These stones are set aside for a short period of months to allow the radioactivity to decay, making the stone safe for buyers to own and wear.
Hardness
- Topaz is a quite-hard mineral, with a rating of 8 on the Mohs hardness scale. Blue topaz shares similar characteristics with diamond; both are very hard stones that can be split with a single blow. Blue topaz has what is known as a "basal cleavage," which is the property of the stone to split along horizontal crystalline planes. Although the stone itself is hard, it should be protected from very hard blows to prevent cracking or splitting.
Size and Clarity
- Natural topaz stones can be quite large; specimens larger than 100 carats have been recorded. The rarer the natural color, however, the smaller the stone will be. In stones of rarer colors, such as pink or red, more inclusions are acceptable. The more common colorless topaz used to make blue topaz is generally quite clean, with a normally vitreous luster -- it has the look of glass.
Specific Gravity
- Specific gravity is based on the density of an object -- meaning that two gemstones of the same size can have different weights. A stone with higher specific gravity can be smaller than a stone with of lower specific gravity, even if they have the same carat weight. Because of this, specific gravity is an instrumental measure in gemstone identification. Topaz has a specific gravity ranging from 3.4 to 3.6. A true topaz would be larger than a sapphire of the same weight, because the sapphire has a higher density.

Gemology