Amethyst, the popular purple variety of quartz, is highly valued in jewelry and decorative objects for its vibrant color and clarity. Understanding its physical attributes is important for appreciating its limits and ensuring its long-term integrity. A gemstone’s strength is determined by its resistance to scratching, its capacity to withstand impact, and its stability when exposed to environmental factors. These properties collectively determine how well the material endures daily wear and maintains its original brilliance.
Measuring Scratch Resistance (Hardness)
A gemstone’s ability to resist scratching is measured by its hardness, quantified using the Mohs Scale of Mineral Hardness. This ten-point relative scale tests a mineral’s ability to scratch another material. Amethyst, a member of the quartz family, possesses a hardness rating of 7. This rating indicates a high resistance to surface abrasion, making it suitable for jewelry like rings that encounter frequent contact.
The Mohs rating of 7 means amethyst is harder than most common household dust and airborne grit, which often consist of softer materials or quartz particles. This protects the amethyst from daily abrasion that might dull softer gems. However, the Mohs scale is not linear, and the difference in hardness between a 7 and a stone rated 8 or higher is significant. Amethyst can still be scratched by harder gemstones, such as topaz (8), corundum (9), or diamond (10).
Resistance to Breaking (Toughness and Fracture)
Toughness is separate from hardness, referring to a gemstone’s resistance to breaking, chipping, or fracturing when subjected to sudden force or impact. Amethyst exhibits good toughness, contributing to its durability in various jewelry settings. This resilience is partly due to its crystalline structure, which does not contain cleavage planes.
Cleavage is the tendency of a mineral to break along smooth, flat surfaces of structural weakness. Since amethyst lacks this characteristic, it will not easily split along predetermined internal lines when struck. Instead, a strong impact causes a conchoidal fracture, resulting in curved, shell-like breakages. The stone is still vulnerable to sharp, direct blows that could cause chipping, particularly along the girdle or facets.
Environmental Stability (Heat, Light, and Chemicals)
Amethyst stability is influenced by its reaction to external conditions like extreme heat, intense light, and chemical exposure. Amethyst is sensitive to heat, which can lead to permanent color alteration. When heated above 300 degrees Celsius, the purple color center, caused by trace iron impurities, can be destroyed. This process is commonly used to intentionally change the stone’s color to yellow-orange citrine or, less frequently, green prasiolite.
Sudden or rapid temperature changes, known as thermal shock, can also induce internal stress that results in fracturing. Prolonged exposure to intense ultraviolet (UV) light, such as direct sunlight, can cause the purple color to gradually fade over time. This fading is typically slow and more pronounced in lighter stones, representing a change in the stone’s chemical structure.
Amethyst is generally resistant to most common household chemicals, contributing to its overall wearability. However, the stone is susceptible to damage from more aggressive substances. Harsh chemicals like hydrofluoric acid, ammonium fluoride, and strong alkaline solutions can etch or corrode the gemstone’s surface.
Daily Wear and Care Guidelines
To maximize the lifespan and beauty of amethyst, specific care practices are recommended that address its physical and environmental vulnerabilities. When cleaning amethyst jewelry, the safest method is using warm water mixed with a mild soap. A soft-bristle brush can then be used gently to remove accumulated dirt and oils from the surface.
Due to the risk of thermal shock and the potential for internal flaws to worsen, steam cleaning is not advised for amethyst. While ultrasonic cleaners are often safe, they should be used with caution for stones that may have internal fractures or have been clarity-enhanced. It is best to remove amethyst jewelry before engaging in strenuous physical activities to avoid accidental sharp impacts that could cause chipping.
For storage, keep amethyst items separate from harder gemstones like diamonds or sapphires. Storing them side-by-side allows harder gems to easily scratch the amethyst surface, dulling its polish. To prevent color fading, the stone should be stored in a cool, dark location away from direct, prolonged exposure to sunlight or strong artificial UV light sources.