The ruby, celebrated for its intense red color, is a gemstone that has been valued for centuries. It is composed of corundum, a crystalline form of aluminum oxide, and owes its vibrant hue to the presence of chromium. This material is renowned for its durability, making it a popular choice for jewelry designed for frequent wear. While rubies are exceptionally hard, they are not indestructible. The stone’s material science reveals specific weaknesses that require careful consideration to maintain its integrity.
Understanding Ruby’s Physical Properties: Hardness and Toughness
Rubies derive their reputation for strength from their composition as corundum, a mineral that is second only to diamond in resistance to scratching. This resistance is measured on the Mohs scale of mineral hardness, where the ruby ranks at a 9. This high hardness means that the ruby is highly resistant to surface abrasions and scratches from most common materials, including dust, which often contains particles of quartz (Mohs 7). The tightly packed atomic structure of aluminum oxide contributes to this extreme scratch resistance.
However, the durability of a gemstone is determined by more than just its hardness; it also relies on its toughness. Hardness refers to the resistance to scratching, while toughness describes the stone’s ability to resist breaking, chipping, or fracturing when subjected to impact. Corundum, the mineral group for rubies and sapphires, possesses only moderate toughness, especially when compared to its high hardness. This distinction is significant because a sharp blow can cause a ruby to chip or fracture, even though it cannot be easily scratched.
The difference between these two properties explains why a ruby, despite its excellent scratch resistance, is not immune to damage from a sudden, forceful impact. The internal arrangement of the atoms dictates how the stone responds to stress. While the bonds resist abrasion, the crystal structure has inherent directions vulnerable to a sudden, concentrated force. This moderate toughness means that while a ruby is excellent for daily wear, it is not impervious to all forms of mechanical stress.
The Primary Causes of Ruby Fracture
Fracturing in a ruby most often occurs when the stone’s moderate toughness is overwhelmed by specific external forces. The most immediate cause is a sharp mechanical impact, which can trigger a break along the stone’s internal structural weaknesses. Corundum does not possess true crystallographic cleavage like some other gemstones, but it does exhibit what is known as “parting” or pseudo-cleavage. This is a tendency to separate along planes of weakness, such as twinning planes, when struck with force.
A sharp blow that hits the ruby, particularly near the girdle or a vulnerable point, can exploit these planes of parting, leading to a clean fracture or chip. This damage often occurs when the stone is accidentally knocked against a hard surface. The concentrated energy of the impact exceeds the stone’s limit of resistance, causing the material to yield along its structurally weaker atomic planes.
Another significant vulnerability is thermal shock, which involves rapid changes in temperature. Rubies are generally stable at high temperatures, but a sudden shift from a hot environment to a cold one causes the stone to expand and contract unevenly. This rapid dimensional change creates immense internal stress that can easily exceed the stone’s fracture resistance, leading to cracking. This is why processes like steam cleaning or sudden exposure to a jeweler’s torch must be handled with extreme caution, especially for stones with pre-existing conditions.
Existing internal flaws, called inclusions, further compromise a ruby’s structural integrity. These natural features, such as tiny crystals or trapped liquids, create stress points within the stone’s matrix. If a ruby with inclusions is subjected to impact or thermal shock, the internal flaw acts as a starting point for a crack to propagate, making the stone more vulnerable to breakage. Many rubies undergo treatments, such as fracture filling, and these treated areas are susceptible to damage from heat and chemicals, as the filler material is less durable than the corundum.
Essential Care Practices for Preventing Breakage
Protecting a ruby requires understanding its vulnerabilities to impact and thermal stress, and adapting care practices accordingly. The most effective preventative measure is to remove ruby jewelry before engaging in any activity that risks a hard knock, such as sports, gardening, or manual labor. Since the stone is susceptible to chipping from sharp impact, choosing a protective setting, such as a bezel that fully encircles the gem, can help shield the vulnerable edges and points.
To avoid the risk of thermal shock damage, especially for treated rubies, it is important to keep the gemstone away from sources of extreme or rapid heat changes. For cleaning, the safest method is to use warm water and a mild, non-detergent soap, gently scrubbing the stone with a soft toothbrush. Harsh household chemicals, including chlorine and ammonia, should be avoided, as they can damage the metal setting or compromise certain fracture-filling treatments.
For rubies that have been fracture-filled or oiled, steam and ultrasonic cleaners are not recommended. These high-energy cleaning methods can weaken the enhancements or cause the filling material to degrade. Regular professional inspections, at least once a year, are advised to check for any loosening prongs or settings that could expose the stone to accidental damage. By applying these practical measures, the ruby can maintain its brilliance and integrity.