Topaz is a widely used gemstone, prized for its impressive range of colors, including clear, deep blue, golden yellow, and the rare imperial pink. It is a popular choice for all types of jewelry, frequently appearing in pendants, earrings, and rings worn daily. When selecting a gemstone, durability is a primary consideration regarding how well it will withstand regular wear. This raises the question: is topaz a hard stone that will maintain its luster, or does it require extreme caution?
Understanding Mineral Hardness
Mineral hardness describes a material’s resistance to being scratched or abraded. This property relates entirely to the strength of the chemical bonds within the mineral’s crystal structure, making it distinct from the stone’s overall strength or tendency to fracture.
The most common method for quantifying this scratch resistance is the Mohs scale of mineral hardness. This scale is an ordinal ranking from 1 (the softest, talc) to 10 (the hardest, diamond). Any material on the scale can scratch all materials with a lower number, but it will be scratched by any material with a higher number. This ranking is relative and not linear, meaning the difference in absolute hardness between levels is not uniform.
Topaz on the Mohs Scale
Topaz ranks 8 on the Mohs scale, confirming its status as a hard gemstone with excellent scratch resistance. This high rating means topaz is not easily damaged by abrasive particles encountered in everyday environments.
For example, most household dust contains quartz, which has a Mohs hardness of 7. Since a hardness-8 stone can easily scratch a hardness-7 stone, topaz is well-protected against this common abrasive.
This ranking places topaz among robust gemstones suitable for regular wear. However, topaz is softer than corundum, which includes rubies and sapphires (9), and diamond (10). A stone with a higher Mohs rating, such as a diamond, can easily scratch the surface of topaz if the two stones come into contact during storage or wear.
Beyond Hardness: Factors Affecting Durability
While topaz possesses superior scratch resistance, its overall durability is complicated by cleavage. Cleavage describes a mineral’s tendency to break smoothly along flat planes of structural weakness when subjected to a sharp impact.
A gemstone’s overall durability is a combination of its scratch resistance (hardness) and its resistance to breaking (toughness). Topaz exhibits “perfect basal cleavage,” meaning it has distinct, relatively weak planes within its crystal structure.
If topaz is hit sharply, it is prone to splitting or chipping along one of these planes, regardless of its Mohs hardness rating of 8. This characteristic means topaz has only moderate toughness, despite its exceptional hardness. This structure requires more careful handling than a stone of similar hardness that lacks cleavage.
Gem cutters must carefully orient the stone during faceting to minimize the risk posed by the cleavage plane. Jewelers often recommend setting topaz in protective settings, especially for rings, to shield the sides and edges from accidental blows. The presence of perfect cleavage distinguishes the stone’s surface strength from its resistance to fracture.
Practical Care and Maintenance
The combination of high hardness and distinct cleavage translates directly into specific care requirements for topaz jewelry owners. Cleaning should be done using simple methods, specifically warm water mixed with a mild soap. The jewelry can be gently scrubbed with a soft brush, such as a soft-bristled toothbrush, to remove dirt and oils.
It is advised to avoid using mechanical cleaning devices like ultrasonic cleaners or steam cleaners. The intense vibrations from an ultrasonic cleaner can exploit the perfect cleavage planes, potentially causing the stone to fracture or chip. High heat from a steam cleaner may also stress the stone and cause breaks.
When storing topaz, keep the jewelry separated from other pieces, especially those with a higher Mohs rating like rubies, sapphires, or diamonds. Storing topaz in an individual soft cloth pouch or a separate compartment prevents harder stones from scratching its surface.
Prolonged exposure to intense heat or strong direct sunlight can cause fading in some topaz colors, particularly the yellow-to-brown varieties and some treated blue stones. Therefore, topaz should be stored in a cool, dark place.