Rubies can be the most valuable colored gemstone, based on price-per-carat.1 However, there are a lot of fakes out there, and it can be hard to tell if a ruby is real. Ultimately, the surest way to tell is to take the stone to a licensed jeweler. At home, you can gauge the rubys authenticity by looking at its color and its hardness. Use a 10-power magnifier, if possible, to inspect the ruby up close.