Emeralds, prized for their rich green color, are a variety of the mineral beryl and are among the world’s most valuable gemstones. The durability of any gemstone is a primary concern for jewelry owners, especially when considering a precious stone for regular wear. Understanding an emerald’s longevity requires examining its physical properties, specifically its hardness and toughness.
Measuring Hardness: The Mohs Scale
The resistance of a gemstone to scratching is measured using the Mohs scale of mineral hardness, which ranges from 1 (softest) to 10 (hardest, like diamond). Emeralds generally rank between 7.5 and 8 on this scale, indicating a high degree of surface hardness. This ranking means an emerald resists scratching from most common materials, including typical metal jewelry settings.
Emerald’s scratch resistance stems from its composition as beryl. Quartz, a major component of dust and grit, registers a 7 on the Mohs scale. Since emerald is harder than quartz, it is protected from the abrasive effects of everyday airborne particles that can dull softer stones. However, the Mohs scale only measures resistance to abrasion and does not account for the gem’s resistance to impact or fracture.
Toughness vs. Hardness: Understanding Emerald’s Vulnerability
The most significant factor affecting an emerald’s durability is its toughness, which is its ability to resist breaking, chipping, or fracturing when struck. Despite their good hardness, emeralds possess only fair to poor toughness, making them more susceptible to impact damage. This comparative weakness is primarily due to the unique internal characteristics of the stone.
Natural emeralds are classified as a Type III gemstone, meaning they almost always contain a significant number of internal flaws, or inclusions. These inclusions, often referred to as jardin (French for “garden”), are networks of fine cracks, liquid-filled cavities, and trapped crystals. These internal features act as points of structural weakness that can quickly spread into a fracture when the stone is subjected to a sharp blow.
Furthermore, the beryl crystal structure possesses cleavage, which is the tendency to break cleanly along defined planes. When a force is applied, especially near the edges or corners of the cut stone, this internal structure can cause the emerald to split or chip relatively easily. This combination of natural inclusions and inherent cleavage is why an emerald, despite being scratch-resistant, must be handled with care to prevent breakage.
Practical Care and Protection
Because of the emerald’s structural properties—good hardness but poor toughness—protective measures must focus on avoiding impact and extreme conditions. The presence of internal fractures means that emeralds are extremely vulnerable to the rapid pressure changes and vibrations created by ultrasonic cleaners. These mechanical forces can cause existing fissures to widen, potentially leading to a catastrophic break in the stone.
The vast majority of emeralds have been treated with oil or resin to fill surface-reaching fissures and improve clarity, a widely accepted practice in the gem trade. Both steam cleaning and ultrasonic cleaning must be avoided because the heat and solvents can strip away the filling agent. This causes the internal fractures to become immediately visible and the stone to appear cloudy.
Emerald jewelry should only be cleaned using mild soap and room-temperature water, applied gently with a soft brush or cloth. When storing emerald jewelry, keep the pieces separated from harder gemstones, such as diamonds or sapphires, to prevent abrasion. For rings, consider a protective setting style, such as a bezel, which encases the edges of the stone and provides a physical barrier against accidental bumps and chips.