Nature's stained-glass windows are buried in Antarctic ice: Polarizing filters reveal the orientation of crystal grains in thin sections of ice pulled up at the West Antarctic Ice Sheet Divide. The transparent shapes, which appear black in low light, are crystals with an orientation that's perpendicular to the ice slice, and each color corresponds to a different angle relative to the plane of the ice section.
Studying individual ice crystals can yield all sorts of information. For example, thicker ice crystals form in summer, and thinner crystals form in winter, so researchers can look at the size of the crystals--and of the air bubbles in their gaps--to determine when that ice fell as snow.