Emerald is a prized gemstone, admired for its intense green color and historical significance, yet its physical durability is often a major concern. While the gem has a respectable hardness of 7.5 to 8 on the Mohs scale, indicating good resistance to scratching, its internal structure makes it susceptible to sudden breakage. Understanding its specific breakage pattern is paramount to its proper care and handling. This tendency to break makes its toughness, or resistance to breaking, surprisingly low compared to other precious stones.
Understanding Cleavage and Fracture
The way any mineral breaks is categorized by two distinct concepts: cleavage and fracture. Cleavage describes a mineral’s predictable tendency to break smoothly along flat, parallel surfaces. This occurs because the chemical bonds holding the crystal lattice together are weaker in specific directions. The quality and number of cleavage directions are often specified.
Fracture, conversely, is the tendency of a mineral to break along irregular surfaces not aligned with any internal crystalline weakness. This random breakage occurs when applied stress exceeds the strength of the chemical bonds, but there is no specific plane for the break to follow. Common types of fracture are described by the appearance of the broken surface, such as conchoidal (shell-like, curved) or uneven. The difference between cleavage and fracture is a matter of predictability and the smoothness of the resulting surface.
The Breakage Profile of Emerald
Emerald, a variety of the mineral beryl, technically exhibits a type of cleavage, but its overall breakage is dominated by fracture. The crystal structure of beryl possesses an imperfect basal cleavage, meaning it has a theoretical plane of weakness where it can break smoothly. This basal cleavage is along the plane perpendicular to the crystal’s main axis. However, the imperfect nature means that while the structural weakness exists, the gem is not prone to splitting along this plane.
In practice, the most common breakage pattern for emerald is fracture, frequently described as conchoidal or uneven. When subjected to impact, it typically breaks with curved, shell-like surfaces or rough, irregular breaks, rather than splitting along a smooth cleavage plane. This distinction is important because the structural weaknesses causing cleavage are less impactful on durability than the natural flaws that lead to fracture. The gem is far more likely to suffer a random fracture than a clean cleavage split.
Inclusions, Treatments, and Durability
Despite its high Mohs hardness, emerald’s toughness is classified as poor, largely due to pervasive internal flaws. Almost all natural emeralds contain numerous internal characteristics, collectively known by the French term jardin (garden). These inclusions are typically natural fractures, fissures, or liquid-filled cavities formed during the gem’s geological creation. The jardin acts as internal stress points, significantly reducing the stone’s structural integrity and making it highly susceptible to fracture from minor impacts.
Because of this inherent fragility, almost all emeralds are subjected to clarity enhancement treatments to improve appearance and stability. The most common treatments involve filling surface-reaching fractures with substances like colorless cedarwood oil or synthetic resins. The filler seeps into microscopic cracks, reducing the visibility of flaws because its refractive index is close to that of the emerald. This treatment improves clarity, but the stone’s stability relies on the integrity of the filler material. Treated emeralds become vulnerable to damage along filled fracture lines if the filler is removed or compromised.
Essential Care and Handling
The specific breakage profile and treatment sensitivity of emerald dictate a need for careful handling. To avoid damage, emerald jewelry should be stored separately in soft pouches or compartmentalized boxes. This prevents contact with harder gems like diamonds or sapphires, which can easily cause a fracture. When selecting a piece, protective settings such as bezels are often preferred over exposed prong settings, especially for rings, to shield vulnerable areas from accidental impact.
Cleaning methods must strictly avoid any process that could compromise the fracture-filling treatments. Ultrasonic cleaners and steam cleaners are highly discouraged because vibrations or high heat can cause the gem to shatter or remove the filler. The safest cleaning method involves using only lukewarm water mixed with a mild dish soap and gently scrubbing with a soft cloth or toothbrush. Emeralds should also be protected from sudden temperature changes, which can cause thermal shock and exacerbate existing internal fractures.