Friedrich Johann Karl Becke (1855-1931) was an Austrian geologist, mineralogist and petrologist from the University of Prague, who developed a method for determining the relationship between light refraction and refractive index differences observed in microscopic specimens. The phenomenon, which is now referred to as the formation of Becke lines, has been named for him. Becke also conducted important work on metamorphic rock recrystallization, and later contributed to the development of a descriptive terminology and classification of mineral assemblages in metamorphic rocks.