5 ways to spot a fake diamond

"When you're looking at a diamond, there are a few things you'll notice," Hirsch told us. "First, the majority of diamonds are made in nature so that means you're going to see some imperfections in the carbon. A fake stone would be perfect — absolutely perfect."

Hirsch explains that certain lab-grown stones will also look perfect through the loupe, and so you should be cautious before discarding perfect gems. It can be a clue, however, that you should take a closer look or bring the stone to an expert.

Second, observe the diamond's edges. "When you're taking a look at a diamond through a loupe, a real stone is going to have sharp edges, and a fake stone will have rounded edges," Hirsch explained.

Lastly, look at the mounting and etchings, especially any marks that signify what metal was used. "If the metal is gold-plated or silver, chances are it's not a diamond, because why would you put a nice stone mounted in such a cheap metal?" Hirsch said. "Most diamonds are mounted in gold or set in platinum."

"Also take a look at the mounting itself and how that diamond is set," she added. “If the setting looks like it’s of poor quality, that probably means it’s not going to be a real diamond either.”

Breathe hot air on your diamond the same way you would if you were fogging up a bathroom mirror.

"A fake diamond will fog up for a short period of time, whereas a real diamond will not because it won't retain the heat," Hirsch explained.

The way that diamonds reflect light is unique: Inside the stone, the diamond will sparkle gray and white (known as "brilliance") while outside of the gem, it will reflect rainbow colors onto other surfaces (this dispersed light is known as "fire").

A fake diamond will have rainbow colors that you can see inside the diamond.

"People have a misconception that diamonds sparkle like a rainbow, but they don't," Hirsch said. "They do sparkle, but it's more of a gray color. If you see something with rainbow colors [inside the stone], it could be a sign that it's not a diamond."

Diamonds are so sparkly because of the way they refract and bend light. Glass, quartz, and cubic zirconium may mimic a diamond's brilliance, but they have much lower refractive indexes.

This means that if your stone isn't in a setting, you can place it over a newspaper, and the light will scatter inside the real diamond and prevent a black reflection. A fake diamond will let the black shine through, and you may even be able to read a word through it, depending on the size of the fake stone.

If your diamond is mounted, make sure you can't see through it to the mount itself — that's a very bad sign.

Dylan Roach contributed to this story.