Yes, a diamond can scratch glass. This ability stems from a fundamental property of materials known as hardness, which describes a substance’s resistance to scratching or abrasion.
The Science of Hardness
Hardness in materials science refers to a material’s ability to resist permanent deformation, particularly scratching or indentation. One widely recognized method for measuring this property is the Mohs scale of mineral hardness. Developed in 1812 by German mineralogist Friedrich Mohs, this scale ranks materials from 1 (softest) to 10 (hardest) based on their capacity to scratch one another.
The Mohs scale operates on a simple principle: a harder material will scratch a softer one. This comparative method allows for a relative ranking of mineral scratch resistance. A higher number on the scale indicates greater scratch resistance.
It is important to note that the Mohs scale is ordinal, not linear. This means that the difference in hardness between two consecutive numbers on the scale is not uniform; for example, a diamond (10) is significantly harder than corundum (9) by a much greater margin than corundum is harder than topaz (8). The scale primarily measures how well a material’s surface resists being scratched by a sharp point.
Diamond Versus Glass: The Scratch Test
Diamond holds the highest possible rating on the Mohs scale, scoring a 10. This makes it the hardest known naturally occurring substance on Earth. Its atomic structure, composed of carbon atoms arranged in a robust cubic crystal lattice, provides its exceptional strength and resistance to scratching.
In contrast, glass is a moderately hard material, typically ranking between 5.5 and 6.5 on the Mohs scale, depending on its specific composition. Standard window glass often has a Mohs hardness of about 6.5. Because diamond’s hardness (10) significantly surpasses that of glass, a diamond will effortlessly scratch glass.
When a diamond is drawn across a glass surface, its sharper, harder facets can overcome the molecular bonds within the glass, leaving a visible and permanent mark. While a diamond can make a scratch line, glass being brittle, will crack along that scratch by stress concentration if bent slightly.
Beyond the Scratch: Practical Uses
The extreme hardness of diamonds makes them invaluable beyond their aesthetic appeal. In various industries, diamonds are extensively used in cutting, grinding, and polishing tools. Diamond-tipped saw blades and drill bits are routinely employed to cut through exceptionally hard materials such as stone, concrete, and even other metals.
Industrial-grade diamonds, which often include synthetic diamonds, are also incorporated into abrasive wheels and polishing compounds. These tools can precisely shape and finish materials that would quickly dull or damage conventional abrasives. The unparalleled wear resistance of diamond ensures that these tools maintain their effectiveness over prolonged use.
Furthermore, the ability of diamond to scratch glass has traditionally been used as a basic test for distinguishing genuine diamonds from imitations. However, this method is not definitive, as other materials like moissanite and cubic zirconia, which are also harder than glass, can produce similar results. The practical applications of diamond’s hardness highlight its importance across diverse technological and manufacturing sectors.