Topaz in its natural state is colorless, often with a greyish cast. It also occurs as a golden brown to yellow which makes it sometimes confused with citrine, a less valuable gemstone. The specific gravity of all shades of topaz, however, means that it is considerably heavier than citrine (about 25% per volume) and this difference in weight can be used to distinguish two stones of equal volume. Also, if the volume of a given stone can be determined, its weight if topaz can be established and then checked with a sensitive scale. Likewise, glass stones are also much lighter than equally sized topaz.
Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F, OH)2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue, golden brown to yellow orange. Topaz is often treated with heat, or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.
Although it is often associated with golden yellow and blue, it comes in a variety of colors, including colorless. The rarest are natural pinks, reds and delicate golden oranges, sometimes with pink hues.
Topaz is a nesosilicate mineral. It is one of the hardest naturally occurring minerals, and has a relatively low index of refraction. It occurs in many places in the world.
A variety of impurities and treatments may make topaz wine red, pale gray, reddish-orange, pale green, or pink (rare), and opaque to translucent/transparent. The pink and red varieties come from chromium replacing aluminium in its crystalline structure.
Imperial topaz is yellow, pink (rare, if natural) or pink-orange. Brazilian imperial topaz can often have a bright yellow to deep golden brown hue, sometimes even violet. Many brown or pale topazes are treated to make them bright yellow, gold, pink, or violet colored. Some imperial topaz stones can fade on exposure to sunlight for an extended period of time. Naturally occurring blue topaz is quite rare. Typically, colorless, gray, or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue. Mystic topaz is colorless topaz which has been artificially coated via a vapor deposition process giving it a rainbow effect on its surface.
Although very hard, topaz must be treated with greater care than some other minerals of similar hardness (such as corundum) because of a weakness of atomic bonding of the stone’s molecules along one or another axial plane (whereas diamonds, for example, are composed of carbon atoms bonded to each other with equal strength along all of its planes). This gives topaz a tendency to break along such a cleavage plane if struck with sufficient force.
Topaz has a relatively low index of refraction for a gemstone, and so stones with large facets or tables do not sparkle as readily as stones cut from minerals with higher refractive indices, though quality colorless topaz sparkles and shows more “life” than similarly cut quartz. When given a typical “brilliant” cut, topaz may either show a sparkling table facet surrounded by dead-looking crown facets or a ring of sparkling crown facets with a dull well-like table.