Moissanite is incredibly hard. It reaches a 9.25 out of 10 on the mohs scale of hardness. This means that it's the second hardest gemstone used in jewelry besides diamonds (which are a 10 out of 10).
But what does this mean? Most people think hardness has to do with "what would happen if I hit this with a hammer?". However, what it actually means is how hard it is to scratch something. If you took a knife to moissanite it would be almost impossible to put any scratches in it. This puts moissanite at a huge advantage when comparing it to cubic zirconium (CZ), fake glass diamonds, sapphire, and topaz.