Tuesday, June 25, 2024

How hard is tanzanite on the mohs scale?

Tanzanite’s Mohs Scale Rating

Tanzanite, a captivating gemstone renowned for its unique blue-violet hue, is a relative newcomer to the world of gemstones, having been discovered in the 1960s in the Merelani Hills of Tanzania. One of the key aspects gemologists and jewelers consider when evaluating a gemstone is its hardness, which is measured using the Mohs scale of mineral hardness. Understanding Tanzanite’s Mohs scale rating is essential for its use in jewelry, as it influences everything from design to maintenance.

The Mohs scale, devised by the German mineralogist Friedrich Mohs in 1812, rates minerals on their ability to scratch one another. The scale ranges from 1 (softest) to 10 (hardest), with each mineral able to scratch those below it on the scale. Tanzanite ranks at about 6.5 to 7 on the Mohs scale. This indicates that while Tanzanite is relatively hard and durable, it is not as hard as other popular gemstones such as diamonds (Mohs hardness of 10), sapphires (Mohs hardness of 9), or rubies (Mohs hardness of 9).

Comparison with Other Gemstones

To provide context for Tanzanite’s hardness, it’s helpful to compare it with other commonly used gemstones.

Diamond (10): Diamonds are the hardest known natural material. This unparalleled hardness makes them exceptionally resistant to scratching and ideal for everyday wear, especially in engagement rings.

Corundum (9): This category includes sapphires and rubies, known for their excellent durability. They are second only to diamonds in hardness, making them suitable for daily wear and all types of jewelry.

Topaz (8): Topaz is relatively hard and more durable than Tanzanite, making it less prone to scratches and suitable for rings and other frequently worn jewelry.

Quartz (7): Quartz, including varieties like amethyst and citrine, shares a similar hardness range with Tanzanite. It is relatively resistant to scratches, but still requires careful handling.

Tanzanite (6.5-7): While Tanzanite is harder than many materials, it is more susceptible to scratching and damage compared to the aforementioned gemstones. It requires more cautious handling, especially in rings or bracelets where they are more exposed to impacts.

Feldspar (6): Gemstones like moonstone and labradorite fall into this category. They are softer than Tanzanite and need even more careful handling.

Apatite (5): Softer than Tanzanite, gemstones like apatite are more prone to scratches and are less commonly used in jewelry that is worn daily.

Durability Implications

Tanzanite’s Mohs hardness rating of 6.5 to 7 implies moderate durability. This means that while Tanzanite can withstand daily wear to some extent, it is not as robust as harder gemstones. Therefore, it is more susceptible to scratching, chipping, and abrasion.

The gemstone’s cleavage also affects its durability. Tanzanite has one direction of perfect cleavage, meaning it can split along specific planes if struck with sufficient force. This characteristic necessitates extra caution during handling and setting in jewelry. Jewelers must take care to avoid exerting pressure along the cleavage planes to prevent damage.

Care Instructions

Given Tanzanite’s moderate hardness and cleavage properties, specific care instructions are crucial to maintaining its beauty and longevity:

Avoid Hard Knocks and Pressure: Tanzanite jewelry should be worn with care to prevent hard knocks or pressure, which can cause chipping or cleavage. This is especially important for rings and bracelets.

Store Properly: When not in use, Tanzanite jewelry should be stored separately from other gemstones to avoid scratches. Using a soft cloth pouch or a separate compartment in a jewelry box is recommended.

Clean Gently: Cleaning Tanzanite requires a gentle approach. Use lukewarm soapy water and a soft brush to clean the gemstone. Avoid ultrasonic cleaners and steamers, as the vibration and heat can cause damage.

Avoid Exposure to Chemicals: Tanzanite should not be exposed to harsh chemicals or prolonged direct sunlight, which can affect its color and integrity. Remove Tanzanite jewelry before swimming, cleaning, or applying lotions and perfumes.

Jewelry Design Recommendations

When designing jewelry with Tanzanite, certain considerations can enhance both its beauty and durability:

Protective Settings: Opt for protective settings such as bezel or halo settings, which provide a rim of metal around the gemstone, offering additional protection against impacts and scratches.

Avoid Rings for Everyday Wear: Due to its moderate hardness and cleavage, Tanzanite is best suited for pendants, earrings, and special occasion rings rather than rings intended for everyday wear.

Choose Lower-Impact Jewelry Types: Necklaces and earrings are less likely to encounter hard impacts compared to rings and bracelets. These designs can help preserve Tanzanite’s appearance and longevity.

Accent Stones: Tanzanite can be beautifully complemented by harder gemstones like diamonds or sapphires. These can act as accent stones that not only enhance the overall design but also offer a protective buffer around the Tanzanite.

See Also: What is December 29 Birthstone?

Treatment Effects

Most Tanzanites on the market have undergone heat treatment to enhance their color, a common and accepted practice in the gemstone industry. This treatment is stable and permanent, meaning it does not negatively affect the stone’s durability if done correctly. However, it is important to note that Tanzanite should not be subjected to high heat or sudden temperature changes after the treatment, as this can potentially cause damage.

Some Tanzanites may also be treated for clarity, although this is less common. Such treatments might involve fracture filling or other techniques that can impact the stone’s stability. Buyers should be aware of these treatments, as they may require additional care.

Repair and Maintenance

Over time, Tanzanite jewelry may require professional repair or maintenance to address wear and tear:

Polishing: Scratches on Tanzanite can often be polished out by a professional jeweler. Regular polishing can help maintain the stone’s luster and appearance.

Re-cutting: In cases of significant damage, re-cutting the gemstone may be necessary. This process involves removing the damaged area and re-faceting the stone, which can reduce its size but restore its beauty.

Re-setting: If the setting becomes loose or damaged, a jeweler can re-set the Tanzanite to ensure it is securely held. This is particularly important for protective settings like bezels.

Regular Inspections: Regular inspections by a professional jeweler can help detect and address potential issues early, such as loose settings or minor chips, before they become major problems.


Tanzanite’s unique and captivating beauty, coupled with its moderate hardness on the Mohs scale, makes it a beloved choice for many jewelry enthusiasts. However, its relative softness and cleavage require mindful handling and specific care to maintain its allure over time. By understanding its properties, choosing appropriate jewelry designs, and adhering to proper care and maintenance practices, Tanzanite can be enjoyed for generations, retaining its mesmerizing charm and elegance.

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