Handling the Hardness of Glass

The simplest way to explain this is to compare the hardness of glass to the universally used “Mineral Hardness Scale called Mohs.” Developed by the German mineralogist Friedrich Mohs back in 1812, this scale measures the relative hardness of natural minerals on a scale of 0 to 10, with 10 being a diamond (the hardest of all known natural minerals). Although glass is manmade from a mixture of minerals, it is not considered a natural mineral and would not normally be measured on the Mohs scale. If it was, however, this is how it would rank on the hardness scale against these common minerals.

• Soapstone – 1
• Slate – 2.4 to 4
• Marble – 3 to 4
• Limestone 3 to 4
• Travertine – 4 to 5
• Glass – 5.5 to 6
• Sandstone – 6 to 7
• Granite – 6 to 7
• Natural Quartz – 7
• Topaz – 8
• Corundum – 9
• Diamond – 10

Now for the most important fact that everyone working with glass needs to know: Every mineral that has a hardness rating above glass is able to scratch glass. Each increase of one on the Mohs hardness scale means that the next hardness step is approximately double. For example, granite is almost twice as hard as glass. In other words, granite will easily scratch glass, but glass will not scratch granite. There are many more manmade materials that will scratch glass, but in the natural mineral world, only the ones above a rating of 5.5 to 6 will do this.