Formula: SiO₂

Mohs: 7

The humble chunk of amethyst you’re holding has a long legacy. It was once among the most prized gemstones like emeralds, sapphires, and diamonds, despite now being more common as a gift shop souvenir. That’s partly because it became much less rare when deposits were discovered in Brazil, but the folks who turn their noses up at amethyst are missing out.

For starters, the way these stones form is wild. They gain their deep purple hue from an unexpected source - radiation. Underground isotopes of things like uranium and potassium emit radiation that ionizes iron trapped inside the quartz, creating charged atoms that reflect purple light. But don’t worry, the pretty purple crystal you’re holding is perfectly safe!