Mohs Scale of Hardness and Alexandrite

Scale Range and Gemstone Examples:

• The scale goes from 1 (softest) to 10 (hardest).
• Common gemstone examples include talc at 1, gypsum at 2, calcite at 3, fluorite at 4, apatite at 5, orthoclase (feldspar) at 6, quartz at 7, topaz at 8, corundum (rubies and sapphires) at 9, and diamond at 10.

Relative Hardness:

• The Mohs Scale is relative, not a linear or proportional one. For example, a diamond (10) is not twice as hard as a corundum (9), but significantly harder.

Alexandrite’s Mohs Hardness Rating

Rating Overview: Alexandrite has a Mohs hardness rating of 8.5. The Mohs Scale, ranging from 1 (softest) to 10 (hardest), is a standard measure used to determine a mineral’s resistance to scratching.

Comparison with Other Gemstones: With a rating of 8.5, Alexandrite is one of the harder gemstones, comparable to topaz, and more scratch-resistant than softer minerals like quartz (rated at 7). It falls just below sapphire and ruby, both rated at 9, and is significantly less hard than diamond, which is at the top of the scale with a rating of 10.

Implications of Alexandrite’s Hardness

Durability for Jewelry: Alexandrite’s high hardness makes it suitable for everyday wear. It is resistant to scratches and abrasions, making it a practical choice for various jewelry pieces, including those that endure more direct wear, like rings and bracelets.

Jewelry Design Considerations: The high hardness rating allows for versatility in jewelry design. Alexandrite can be incorporated into elaborate designs without much concern for the gemstone getting easily scratched.

Care and Maintenance: Despite its hardness, Alexandrite, like all gemstones, should be cared for to maintain its shine and clarity. It should be stored separately to avoid contact with harder substances and cleaned gently with a soft brush and mild soap.

Alexandrite’s Place on the Mohs Scale

• Significance: Alexandrite’s position on the Mohs scale at 8.5 is a testament to its suitability as a durable gemstone. It can withstand daily exposure without significant wear, which is a desirable quality for fine jewelry.
• Considerations for Buyers: For buyers, the hardness rating is a key factor in decision-making. It assures longevity and enduring beauty, especially for pieces meant for regular wear.

Understanding the Mohs Scale

Relative Scale: The Mohs Scale measures hardness on a scale from 1 (softest) to 10 (hardest). However, it’s important to note that this scale is relative and not linear. The difference in hardness between each number isn’t consistent.

Hardness vs. Toughness: The Mohs Scale specifically measures scratch resistance, not the overall durability of a gemstone. It doesn’t account for a gemstone’s toughness (resistance to breaking, chipping, or cracking) or stability (resistance to chemical or thermal damage).

Limitations in relation to Alexandrite

Alexandrite’s Hardness: Alexandrite ranks high on the Mohs scale at 8.5, indicating excellent resistance to being scratched. However, this doesn’t necessarily imply that the gemstone is immune to other forms of wear or damage.

Toughness and Stability Considerations: Despite its high hardness, Alexandrite’s toughness is only fair to good. This means it can still be susceptible to chipping or breaking if subjected to sharp impacts or rough handling.

Sensitivity to Environmental Factors: The Mohs Scale doesn’t indicate how Alexandrite will react to various environmental factors, such as exposure to high temperatures or chemicals, which can potentially affect its color or structural integrity.

Practical Implications for Alexandrite Owners

Careful Handling: Owners of Alexandrite jewelry should understand that while their gemstone is resistant to scratches, it should still be handled carefully to avoid impacts or pressure that could cause chipping or breaking.

Appropriate Settings and Storage: Considering Alexandrite’s good but not perfect toughness, choosing protective settings and providing careful storage away from harder materials can help prevent damage.

Regular Professional Check-Ups: Routine inspections by a professional jeweler can help in early identification of any potential damage or weaknesses, particularly in the gemstone’s setting.