Look closely at the picture above. You’ll see perfect hexagons lying among the columns on the ground. Are these the remains of a quarry? Did humans craft these perfectly hexagonal columns? No. These hexagons are at the Devil's Postpile National Monument, a rock formation in California. They’re totally natural.
Amazing But True
The Devil’s Postpile was formed hundreds of thousands of years ago, when molten lava cooled slowly and at a regular temperature. Scientists call this sort of formation basalt columns. In addition to hexagons, basalt columns can form pentagons, quadrilaterals, heptagons, and triangles. Basalt columns exist all over the world and are always a sign of ancient volcanic activity.
Lava isn’t the only natural material that forms perfect polygons. Salt crystals have square surfaces, and quartz crystals often contain rectangles and triangles. Even living things make polygons. For instance, bees make their honeycombs from perfectly constructed hexagons. Some species of starfish are shaped like pentagons. Look closely at the world around you. You’ll be surprised by how many polygons you can identify.
See for yourself: https://www.youtube.com/watch?v=lE-8QuBDkkw
Mineralogists study minerals and crystals and how they form. Check out these links on the shapes of crystals from the Smithsonian Institution in Washington, D.C.