The second hardest gemstone is Corundum, which includes well-known precious stones such as sapphires and rubies.
Corundum holds a remarkable rank of 9 on the Mohs scale of mineral hardness, positioning it as the second hardest natural gemstone. Its exceptional hardness is a primary reason for its durability and suitability for various types of jewelry, making it a popular choice for engagement rings and other frequently worn pieces.
Understanding Gemstone Hardness
Gemstone hardness is typically measured using the Mohs scale of mineral hardness. Developed by German mineralogist Friedrich Mohs in 1812, this scale assesses a mineral's resistance to scratching by another material. The scale ranges from 1 (softest, like talc) to 10 (hardest, diamond). It's important to note that the Mohs scale is ordinal, meaning the steps are not of equal magnitude; for example, a diamond (10) is significantly harder than corundum (9) than corundum is harder than topaz (8).
The hardness of a gemstone is crucial for:
- Durability: Harder gemstones are more resistant to scratches from everyday wear and tear.
- Longevity: They maintain their polish and brilliance longer.
- Jewelry Suitability: Gemstones used in rings, especially, benefit from high hardness to withstand impacts and abrasion.
Corundum: The Second Hardest
Corundum is an aluminum oxide mineral (Al₂O₃) that crystallizes in the trigonal system. Its impressive hardness, second only to diamond, makes it incredibly valuable.
- Sapphires: These are corundum gemstones known for their wide range of colors, most famously blue. Other sapphire colors include pink, yellow, green, and purple, often referred to as "fancy sapphires."
- Rubies: Rubies are red varieties of corundum. Their vibrant red hue is caused by the presence of chromium. They are one of the most historically significant and highly prized gemstones.
Both sapphires and rubies benefit from corundum's exceptional hardness, ensuring their beauty endures for generations.
Top Hardest Gemstones
To provide context, here's a comparison of the hardest natural gemstones:
| Rank | Gemstone | Mohs Hardness | Key Characteristics |
|---|---|---|---|
| 1 | Diamond | 10 | Pure carbon, supreme hardness, exceptional brilliance. |
| 2 | Corundum | 9 | Aluminum oxide; includes sapphires and rubies; very durable. |
| 3 | Topaz | 8 | Aluminum and fluorine silicate; known for various colors. |
| 4 | Quartz | 7 | Silicon dioxide; common mineral; includes amethyst, citrine. |
The superior hardness of gemstones like corundum means they are less prone to scratching by common materials, including dust particles (which often contain quartz), making them ideal for everyday jewelry wear. This quality contributes significantly to their lasting value and appeal.
