Turquoise is an opaque gemstone celebrated across cultures for its striking color, which ranges from clear sky-blue to greenish-blue hues. Valued for millennia, it features prominently in ancient Egyptian, Chinese, and Native American jewelry and artifacts. As a hydrated phosphate of copper and aluminum, its unique composition gives it both its distinctive appearance and specific physical characteristics. Understanding the physical hardness of turquoise is important for jewelry owners, as this property directly influences the stone’s durability and long-term care requirements.
The Mohs Scale and Turquoise Hardness
The hardness of any mineral is measured using the Mohs scale, a qualitative system that ranks a mineral’s resistance to being scratched. This scale uses ten reference minerals, with 1 being the softest (talc) and 10 being the hardest (diamond). The Mohs scale measures scratch resistance, not compressive strength or resistance to impact.
Natural turquoise generally registers a moderate hardness range between 5 and 6 on this scale. This placement means the stone can be scratched by materials commonly found in everyday life. For comparison, a standard steel nail has a hardness of approximately 6.5, and common glass is around 5.5.
Because of this moderate hardness, turquoise is significantly softer than many other popular jewelry stones. Quartz, a mineral often found in dust, ranks at 7, meaning an abrasive environment can easily scratch untreated turquoise. Diamond, by contrast, is a 10, highlighting the substantial difference in scratch resistance between turquoise and harder gems.
Natural Factors Affecting Durability
The variation in turquoise’s hardness, falling between 5 and 6, results from its intrinsic geological structure. Turquoise is a cryptocrystalline mineral, meaning its crystals are microscopic and densely packed, but the stone often contains varying levels of porosity. Porosity refers to tiny, interconnected spaces within the structure.
Turquoise that is less dense and more porous is often described as “chalky” and can have a hardness closer to 3 or 4, making it vulnerable to damage. Only the highest-grade natural turquoise, which is dense and tightly structured, achieves the maximum hardness of 6. This superior material is less common and commands a higher value.
The presence of a matrix, the dark spiderweb-like veining often seen, is composed of the host rock. However, the overall durability is primarily determined by the density of the copper aluminum phosphate mineral. Greater density translates directly to a higher resistance to abrasion and scratching.
How Treatments Change Hardness
The moderate softness of natural turquoise has led to the widespread commercial practice of stabilization to enhance its durability. Stabilization is a treatment where porous, lower-grade turquoise is impregnated with a bonding agent, typically a clear polymer or epoxy resin. This process is often performed under pressure to force the resin deep into the stone’s microscopic pores.
The primary goal of stabilization is to significantly reduce the stone’s natural porosity and increase its working hardness. By filling the internal voids, the resin solidifies the structure, making the turquoise less susceptible to scratching and chipping. This treatment effectively raises the stone’s functional hardness, making it suitable for jewelry that experiences more wear, such as rings.
Stabilization also prevents external substances from being absorbed, which is a common cause of discoloration in untreated turquoise. Unlike simple dyeing or waxing, the polymer permeates the stone, securing both the hardness and the color.
Caring for Turquoise Jewelry
The moderate hardness of turquoise dictates specific care practices to ensure the stone maintains its color and finish. Due to its position on the Mohs scale, turquoise jewelry should always be stored separately from harder gemstones like diamonds, sapphires, or quartz, which could easily scratch the surface. It is best kept in a soft pouch or a dedicated compartment to prevent abrasion.
The stone’s porosity, even in stabilized material, means it can absorb chemicals and oils that can permanently alter its color. Owners should avoid exposing turquoise to:
- Harsh cleaning solutions.
- Perfumes.
- Hairsprays.
- Prolonged contact with skin oils.
- Perspiration.
Always put on turquoise jewelry after applying cosmetics. Cleaning should be done with only warm water and a mild soap, using a soft cloth or brush to gently wipe the surface. Because the stone or stabilization resins can be sensitive to intense vibrations and heat, ultrasonic and steam cleaners must never be used.