The Properties of Diamonds

Diamonds are found as rough stones and must be processed to create a sparkling gem that is ready for purchase.

Photo courtesy Getty ImagesThese rough stones will become dazzling diamonds after they are cut and polished.

As mentioned before, diamonds are the crystallized form of carbon created under extreme heat and pressure. It's this same process that makes diamonds the hardest mineral we know of. A diamond ranks a 10 on the Mohs Hardness Scale. The Mohs Scale is used to determine the hardness of solids, especially minerals. It is named after the German mineralogist Friedrich Mohs. Here's the scale, from softest to hardest:

1. Talc - easily scratched by the fingernail
2. Gypsum - just scratched by the fingernail
3. Calcite - scratches and is scratched by a copper coin
4. Fluorite - not scratched by a copper coin and does not scratch glass
5. Apatite - just scratches glass and is easily scratched by a knife
6. Orthoclase - easily scratches glass and is just scratched by a file
7. Quartz - (amethyst, citrine, tiger's-eye, aventurine) not scratched by a file
8. Topaz - scratched only by corundum and diamond
9. Corundum - (sapphires and rubies) scratched only by a diamond
10. Diamond - scratched only by another diamond

Even though diamond is only one level higher on the scale than corundum, diamond can be anywhere from 10 to hundreds of times harder than this class of gems.

It is the molecular structure of diamonds that makes them so hard. Diamonds are made of carbon atoms linked together in a lattice structure. Each carbon atom shares electrons with four other carbon atoms, forming a tetrahedral unit. This tetrahedral bonding of five carbon atoms forms an incredibly strong molecule. Graphite, another form of carbon, isn't as strong as diamond because the carbon atoms in graphite link together in rings, where each atom is only linked to one other atom.