Peridot is the gem-quality variety of the mineral olivine, known for its yellowish-green to deep olive hue. This vibrant stone forms deep within the earth and is brought to the surface by volcanic activity. When used in jewelry, its resilience is measured by its scratch resistance, defined by the Mohs scale of mineral hardness. Peridot is rated between 6.5 and 7 on this scale.
Peridot’s Hardness on the Mohs Scale
The Mohs Scale of Mineral Hardness is a qualitative system used to rank a mineral’s resistance to scratching by comparing it to ten reference minerals. Peridot’s rating of 6.5 to 7 places it in the upper-middle range, suggesting good resistance to surface abrasion. Materials softer than peridot will not leave a scratch, allowing the stone to maintain its polish during normal wear.
The Mohs scale is not linear; the difference in hardness between a rating of 9 (sapphire) and 10 (diamond) is much greater than the difference between 6 and 7. Peridot’s rating is similar to common household dust, which often contains quartz (rated 7). Since quartz is ubiquitous, small particles of dust can potentially scratch peridot if the stone is wiped roughly or carelessly.
Peridot is significantly softer than popular gemstones like topaz (8), sapphire (9), and diamond (10). This moderate hardness means peridot is appropriate for various jewelry pieces, but it requires moderate care to prevent surface abrasions from harder stones or materials. Its scratch resistance is sufficient for everyday wear in less exposed settings like earrings and pendants, but rings are more prone to contact with harder objects.
Beyond Scratch Resistance: Toughness and Cleavage
Gemstone durability is a complex measure encompassing both toughness and cleavage, going beyond simple scratch resistance. Toughness describes a gemstone’s ability to resist breaking, chipping, or cracking when subjected to impact or sudden stress. Peridot has a rating of fair to good toughness, meaning it is not as structurally robust as stones with similar hardness, such as jade.
The stone’s crystal structure dictates its cleavage, which is the tendency of a mineral to break along defined planes of weakness. Peridot has an imperfect cleavage plane, meaning it is more susceptible to fracturing from a sharp blow or impact. This structural vulnerability, particularly along the facet edges, is why peridot is prone to chipping despite its moderate Mohs hardness.
Understanding the distinction between hardness and toughness is important. While peridot resists scratching from many common objects, a direct, sharp impact could cause it to cleave or fracture. Therefore, the stone’s overall durability is considered only moderate, especially compared to harder or tougher gems.
Practical Care Guidelines for Peridot Jewelry
The moderate hardness and fair toughness of peridot require specific care to preserve the stone’s beauty. Ultrasonic and steam cleaners are not recommended for cleaning peridot jewelry due to its susceptibility to fracturing from impact and thermal stress. The high-frequency vibrations in ultrasonic machines and the rapid temperature changes of steam cleaning can cause internal flaws to worsen or lead to new fractures.
The safest way to clean peridot is using a solution of mild soap and lukewarm water. Gently brush the stone with a soft cloth or toothbrush to remove dirt, then rinse thoroughly and pat dry. Peridot is also sensitive to various chemicals, including acids like sulfuric acid and prolonged exposure to acid perspiration.
It is advisable to store peridot jewelry separately from other pieces, particularly those containing harder gems like diamonds or sapphires. Placing the peridot in its own soft pouch or separate compartment prevents accidental contact that could easily scratch the surface. Mindful wearing, such as removing rings before engaging in strenuous activities, will also prevent the sharp impacts that could cause chipping or fracture.