FORMULA: CaCO3
MOHS HARDNESS: 3
Calcite is a super common mineral, but there’s more to this crystal than meets the eye. Look through it and you’ll see what we mean. Calcite has a property called birefringence, which means that the structure of the crystal plays tricks with light. The internal structure splits apart the different directions of polarized light that pass through it, resulting in two images.
And this isn’t just a party trick. There’s a chance that the Vikings used calcite to help them navigate. Because sunlight is polarized in a specific way as it enters our atmosphere, you can use directions of polarized light to figure out where the sun is, even when it’s behind clouds or below the horizon. Check out this month’s SciShow Rocks Box video for the details!