* Mohs Hardness Scale: This scale measures a material's resistance to scratching. On this scale, diamond is the hardest at 10, followed by corundum (sapphire and ruby) at 9.
* Vickers Hardness Test: This test measures a material's resistance to indentation. Here, the answer becomes more complex, as different materials can be incredibly strong under pressure, even surpassing corundum. Some contenders include:
* Cubic Boron Nitride (CBN): This material is very hard and resistant to high temperatures, making it valuable for industrial applications.
* Tungsten Carbide: While not as hard as CBN, Tungsten Carbide is still incredibly strong and commonly used in cutting tools and other applications where durability is crucial.
Ultimately, the answer to what is the second hardest thing in the world depends on which definition of "hardness" you're using.
