The question of an emerald’s “strength” is more complex than it first appears. Emeralds are the green variety of the mineral beryl, and they are often considered fragile despite possessing high scratch resistance. Gemstone durability is a combination of three factors: hardness (resistance to scratching), toughness (resistance to breaking or chipping), and stability (resistance to chemicals and heat). For emeralds, a high ranking in one area does not guarantee a high ranking in the others, making it essential to understand their specific physical properties.
Understanding Gemstone Hardness
Hardness in gemology refers to a material’s resistance to abrasion or scratching. This property is measured using the Mohs scale, which ranks minerals from 1 (softest) to 10 (hardest). Emeralds typically fall between 7.5 and 8 on this ordinal scale. This placement means the stone is hard enough to resist scratching from most common household dust (quartz at Mohs 7). It also means that emeralds are significantly harder than many metals used in jewelry settings. However, the scale is logarithmic, meaning the difference in hardness between a 7.5 and a 10 (diamond) is vast. For example, a corundum stone, such as a ruby or sapphire, sits at 9 and can easily scratch an emerald.
The Impact of Internal Structure on Durability
While emeralds are scratch-resistant, their resistance to impact, known as toughness, is generally considered poor. This is the primary reason for their reputation as being brittle. The formation process of natural emeralds often results in numerous internal fractures and mineral inclusions. These internal features are so common that they are romantically referred to as the jardin, or “garden,” within the stone. Although these inclusions give each emerald a unique visual character, they simultaneously introduce structural weak points throughout the crystal lattice.
These flaws act as natural stress concentrators, which can easily extend into a full fracture upon a sharp blow. The beryl crystal structure itself features inherent planes of cleavage, meaning the crystal has preferred directions along which it can split when struck. The combination of these internal flaws and cleavage planes makes emeralds highly susceptible to chipping or breaking. This is particularly true when subjected to sudden impact or rapid changes in temperature (thermal shock). Therefore, an emerald with fewer inclusions will inherently possess greater toughness than a heavily included stone.
Enhancements and Their Effect on Strength
The prevalence of surface-reaching fractures in emeralds has led to the nearly universal practice of clarity enhancement. This process involves filling the microscopic fissures with colorless substances to improve the gem’s transparency and overall appearance. Industry estimates suggest that well over 90% of natural emeralds have received some form of fracture-filling treatment.
The most traditional filler is natural cedarwood oil, which is heated and pressurized to seep into the tiny cracks. More modern enhancements use synthetic resins and polymers, which are often more stable than oil. While these fillers visually mask the fractures, they do not fundamentally repair the stone’s structural integrity. The presence of these fillers introduces new vulnerabilities, especially to heat and chemicals. High temperatures or harsh chemicals can cause the fillers to degrade, dissolve, or discolor, compromising the stone’s appearance and requiring careful handling.
Practical Care and Maintenance
Because of the emerald’s inherent brittleness and the universal use of fracture-filling enhancements, specific care protocols are necessary for long-term preservation. The primary rule is to avoid activities that expose the stone to impact, such as gardening, manual labor, or sports. Rings should be set in protective styles, like bezel settings, which encase the stone’s vulnerable girdle and corners.
Cleaning must be done gently to avoid damaging the fracture fillers. The safest method is to use warm water mixed with a mild dish soap and a soft-bristled brush, followed by a thorough rinse with clean water. It is necessary to avoid two common jewelry cleaning methods: ultrasonic cleaners and steam cleaners. The intense vibrations of an ultrasonic cleaner can exacerbate existing fractures and cause the filler material to leak out. Similarly, the high heat from a steam cleaner can damage or remove the fillers, leading to a sudden loss of clarity. Storing emerald jewelry separately in a soft pouch prevents contact with harder gemstones, such as diamonds.