Turquoise is a prized gemstone, cherished for its unique blue-green hues. This vibrant color is a direct result of its chemical makeup, as it is a hydrated phosphate of copper and aluminum. For anyone considering ownership, understanding the stone’s physical properties is important for preservation. Its resistance to damage, especially scratching, directly influences how it should be worn and cared for over time.
Defining Hardness: The Mohs Scale
Mineral hardness refers to a material’s resistance to scratching or abrasion. This property is measured using the Mohs Scale of Mineral Hardness, developed by German mineralogist Friedrich Mohs in 1812. The scale is an ordinal ranking from 1 to 10, which assesses the relative ability of one substance to scratch another. It operates on the principle that a harder material will visibly scratch a softer one.
The Mohs scale is relative, not absolute, meaning the difference in actual hardness between two consecutive numbers is not uniform. For example, the difference in hardness between a mineral rated 9 and 10 is much greater than the difference between 1 and 2. The scale is anchored by Talc (1) and Diamond (10).
Turquoise’s Specific Hardness Rating
Turquoise typically registers a rating between 5 and 6 on the Mohs scale of mineral hardness. This places it in the moderately soft category of gemstones, indicating it has a reasonable but not high resistance to scratching. The precise rating can vary slightly depending on the specific mineral composition, with some softer specimens falling below 5 and the hardest, gem-quality pieces reaching 6.5.
A hardness of 5 to 6 means turquoise can be scratched by several common household materials and environmental elements. A steel knife blade, for instance, has a hardness of around 5.5, meaning it could easily scratch most turquoise. Ordinary dust often contains minute particles of Quartz (hardness 7), making turquoise vulnerable to scratching from improper cleaning or daily exposure to airborne grit.
Practical Durability and Maintenance
The moderate hardness of turquoise translates directly into specific requirements for its care and handling. Because the stone is relatively soft, it should not be worn during activities that could expose it to impacts or abrasion, such as manual labor or exercise. When not being worn, turquoise jewelry must be stored separately from harder gemstones like sapphires (9) or topaz (8) to prevent surface damage.
Turquoise is also a porous stone, which means it can easily absorb chemicals, oils, and liquids, leading to discoloration. This porosity makes the stone vulnerable to damage from substances like perfumes, cosmetics, household cleaners, and even natural skin oils or perspiration. Exposure to high heat or prolonged direct sunlight can also cause the color to fade or the stone to become brittle.
Cleaning turquoise requires a gentle approach to preserve its color and integrity. The safest method involves using a soft, damp cloth with a small amount of mild, non-detergent soap, followed by quickly drying the stone. Owners must avoid ultrasonic cleaners and steam cleaners, as the vibrations and heat from these devices can cause internal fractures or damage any stabilizing treatments the stone may have received.