Birefringence is an optical property of certain materials that causes them to refract light in two different directions. This phenomenon occurs when light passes through a material with a unique internal structure, leading to two distinct indices of refraction. Common examples of birefringent materials include calcite and quartz. When light enters a birefringent material, it splits into two rays, each traveling at different speeds and angles. This results in the appearance of double images when viewed through the material. Birefringence is utilized in various applications, including polarizers and optical devices, to manipulate light for scientific and industrial purposes.