Turquoise is a hydrated phosphate of copper and aluminum, a chemical composition that gives the mineral its distinctive opaque blue-to-green coloration. This stone has been prized as a decorative material and gemstone for thousands of years. The beauty of turquoise makes it a popular choice for jewelry, but its physical properties often lead people to question its durability. This article addresses the common perception of turquoise as a “soft” stone by examining its scientific classification of hardness.
Defining Mineral Hardness
Mineral hardness is a measure of a substance’s resistance to scratching or abrasion. It is not a measure of brittleness or resistance to breaking, which are distinct concepts known as toughness. The standard method for classifying this property is the Mohs Scale of Hardness, developed in 1812 by German mineralogist Friedrich Mohs.
The Mohs scale ranks minerals from 1 (softest) to 10 (hardest) based on which substance can visibly scratch another. It is an ordinal scale, meaning the intervals between the numbers are not equal; for example, a diamond (10) is significantly harder than corundum (9) than corundum is than topaz (8). To provide a sense of scale, a human fingernail ranks around 2.5, while quartz, the most common mineral on Earth, serves as a benchmark at 7 on the scale.
The Hardness Rating of Turquoise
Turquoise occupies a moderate position on the scale, generally ranging from 5 to 6 in hardness. This means that while it is harder than very soft minerals like talc (1) or gypsum (2), it is considerably softer than the gemstones typically used in engagement rings, such as sapphire (9) or diamond (10). Its rating places it slightly above common glass, which is often around 5.5.
The specific hardness can vary depending on the stone’s formation, with some softer, chalkier specimens barely exceeding 2, while the finest gem-quality material can reach just under 6. This moderate hardness is the reason for the stone’s reputation as being “soft” in the jewelry trade. It is significantly less resistant to abrasion than the high-ranking minerals used for daily-wear jewelry.
Implications for Wear and Care
The Mohs rating of 5 to 6 has direct practical consequences for how turquoise jewelry must be worn and maintained. Its moderate hardness means the stone is vulnerable to scratching from common materials, including household dust, which often contains tiny particles of quartz (7). This susceptibility to abrasion necessitates careful handling to preserve the stone’s polished surface.
Beyond its hardness, turquoise is also a porous material. Its porosity allows it to absorb liquids and chemicals, which can cause discoloration or staining. Exposure to perfumes, lotions, body oils, and even sweat can alter the stone’s color over time.
To properly care for turquoise, it should be cleaned gently with a soft, damp cloth and mild, unscented soap, but never soaked in water. Ultrasonic cleaners, steam cleaners, and harsh chemicals must be avoided entirely due to the risk of irreparable damage to the porous structure. When storing turquoise pieces, they should be kept separate from harder jewelry items, like diamonds or rubies, to prevent contact scratches.