Blue topaz is one of the most recognizable and widely used colored gemstones in modern jewelry. Its appealing range of blue hues and relatively affordable price point have secured its place as a staple in the global gem market. The stone’s popularity allows it to be fashioned into various cuts and settings, offering consumers an accessible way to wear a striking blue gem.
The Mineral Composition and Properties of Topaz
Topaz is classified as a nesosilicate mineral, meaning its structure is built around isolated silica tetrahedra. Its chemical formula is represented as Al₂(SiO₄)(F,OH)₂, indicating it is an aluminum and fluorine silicate that may also contain a hydroxyl group. This composition gives topaz a naturally high level of hardness, which is a desirable trait for any gemstone.
The mineral ranks as an 8 on the Mohs scale of hardness, making it highly resistant to scratching and suitable for daily wear. However, topaz possesses perfect basal cleavage, meaning the stone has internal planes of weakness. A sharp blow or impact along these planes can cause it to crack or fracture despite its overall durability.
How Blue Topaz Gets Its Color
Nearly all blue topaz available today, from the palest to the deepest shades, is the result of a stable treatment process. Naturally occurring blue topaz is extremely rare and typically only exhibits a very light, pale blue color. The process starts with colorless or very pale topaz material, which is plentiful and inexpensive.
This colorless material is subjected to irradiation, which alters the crystal structure and creates color centers within the stone. The specific type of irradiation used determines the initial color change. Often, the initial result of irradiation is a brown, yellow, or grayish color.
The second and final step is heat treatment, also called annealing, which stabilizes the color and removes any unwanted yellow or brown components. The precise duration and intensity of both the irradiation and the heating are carefully controlled to produce the desired final shade of blue. This two-step process yields a permanent color enhancement that will not fade under normal wearing conditions.
Grading Blue Topaz: Understanding Trade Names
The various shades of treated blue topaz are sorted into three primary commercial trade names, which are based on the depth and saturation of the color. The lightest and most common shade is called Sky Blue Topaz. It exhibits a bright, airy blue hue that is often compared to the color of aquamarine.
The next level of saturation is Swiss Blue Topaz, which is a vibrant, medium-dark blue. This shade is often described as an electric or intense blue and is a popular choice for commercial jewelry.
The deepest and richest color is known as London Blue Topaz. London Blue is characterized by a dark, inky blue color that frequently has a slight grayish or greenish undertone. Because achieving this intense saturation requires the longest and most complex treatment, London Blue is generally considered the most valuable of the three commercial blue varieties.
Practical Considerations for Jewelry and Care
Blue topaz is suitable for almost all types of jewelry, including rings subject to daily wear. It holds up well against scratching, which helps maintain its brilliance over time. However, due to its perfect cleavage, the stone is vulnerable to chipping or fracture if it sustains a sharp, hard impact.
To clean blue topaz jewelry, a simple solution of mild dish soap and lukewarm water is recommended. The jewelry can be soaked briefly, and a soft cloth or toothbrush should be used to gently scrub away any dirt or residue. It is important to avoid prolonged exposure to extreme heat, such as that found in ultrasonic cleaners or direct, intense sunlight, as this can potentially affect the stone’s color or cause internal damage.