What is the second strongest mineral? The second strongest mineral on Earth is corundum, which is known for its remarkable hardness and durability. Corundum ranks just below diamond on the Mohs scale of mineral hardness, making it a popular choice for applications requiring robust materials, such as industrial abrasives and gemstones like sapphires and rubies.
Understanding Corundum’s Strength
Corundum is an aluminum oxide mineral that exhibits a hardness of 9 on the Mohs scale, where diamond, the hardest known mineral, scores a perfect 10. This high hardness level makes corundum exceptionally resistant to scratching and abrasion, which is why it is often used in various industrial applications and as a gemstone.
What Makes Corundum So Hard?
The hardness of corundum is attributed to its strong atomic structure. It consists of tightly packed aluminum and oxygen atoms, forming a hexagonal crystal lattice. This structure not only contributes to its hardness but also makes it highly stable under extreme conditions.
- Atomic Structure: Hexagonal close-packed
- Chemical Composition: Al₂O₃ (aluminum oxide)
- Density: Approximately 4.0 g/cm³
Applications of Corundum
Corundum’s durability and hardness make it invaluable in several industries:
- Abrasives: Used in sandpapers and grinding wheels.
- Gemstones: Sapphires and rubies, both varieties of corundum, are prized for their beauty and hardness.
- Industrial Uses: Employed in cutting tools and machinery parts due to its wear resistance.
Comparing Hardness: Corundum vs. Other Minerals
To understand corundum’s position as the second strongest mineral, it is helpful to compare it with other minerals on the Mohs scale:
| Mineral | Mohs Hardness | Common Uses |
|---|---|---|
| Talc | 1 | Baby powder, lubricants |
| Gypsum | 2 | Plaster, drywall |
| Calcite | 3 | Cement, agriculture |
| Fluorite | 4 | Metallurgy, optics |
| Apatite | 5 | Fertilizer, toothpaste |
| Orthoclase | 6 | Ceramics, glass |
| Quartz | 7 | Glassmaking, electronics |
| Topaz | 8 | Jewelry, industrial cutting |
| Corundum | 9 | Abrasives, gemstones |
| Diamond | 10 | Cutting tools, jewelry |
This table highlights corundum’s superior hardness compared to most other minerals, with only diamond surpassing it.
People Also Ask
What are the primary uses of corundum?
Corundum is primarily used as an abrasive due to its hardness. It is also a popular choice for gemstones, with sapphires and rubies being the most famous varieties. In industry, corundum is used in cutting tools and machinery parts due to its wear resistance.
How does corundum compare to diamond?
While both corundum and diamond are extremely hard, diamond is the hardest known mineral with a Mohs hardness of 10, whereas corundum has a hardness of 9. Diamond’s superior hardness makes it more effective for cutting and drilling applications, but corundum is more abundant and affordable for general industrial use.
Why are sapphires and rubies considered corundum?
Sapphires and rubies are both varieties of corundum. The difference lies in their trace elements: rubies contain chromium, which gives them their red color, while sapphires can be a range of colors depending on the trace elements present, with blue being the most common.
Can corundum scratch glass?
Yes, corundum can easily scratch glass because glass typically has a hardness of about 5.5 on the Mohs scale, which is significantly lower than corundum’s hardness of 9.
Are there synthetic versions of corundum?
Yes, synthetic corundum is produced for both industrial and gemological purposes. Synthetic sapphires and rubies are widely used in jewelry and as durable materials in various technologies, offering similar properties to their natural counterparts at a lower cost.
Conclusion
Corundum’s status as the second strongest mineral underscores its importance in both industrial and gemological contexts. Its exceptional hardness makes it a versatile material, from crafting beautiful gemstones to serving as a critical component in cutting tools. Understanding the properties and applications of corundum not only highlights its practical value but also enriches our appreciation of the natural world’s complexities. For further exploration, consider delving into topics like the Mohs scale of mineral hardness or the process of synthetic gemstone production.
