Feldspar is the most common type of mineral in Earth's crust, making up about 60% of the rocks near the surface. If you've ever picked up a random rock and noticed shiny, smooth crystals embedded in it (often white, pink, or gray), you were probably looking at feldspar.

Feldspar forms when molten rock cools and hardens, which is why you find it in granite countertops, monument stones, and the rocks that make up mountains.

Geologists use feldspar to understand how old rocks are and how they formed. Feldspar also has important practical uses: manufacturers use ground-up feldspar to make glass, pottery, and ceramics. The smooth glaze on a coffee mug likely contains feldspar. Ancient potters discovered that adding feldspar to clay made their pottery stronger and gave it a beautiful finish.

Feldspar actually refers to a whole family of related minerals with similar crystal structures but slightly different chemical compositions. The most common types are orthoclase (usually pink or white) and plagioclase (usually white or gray). Next time you see a speckled rock, look closely at those shiny bits: you're probably seeing one of the planet's most abundant minerals.