- streaks or irregularly shaped masses in an igneous rock that differ in texture or composition from the main mass.
- the visible streaks in a turbulent, transparent fluid, each streak being a region that has a density and index of refraction differing from that of the greater part of the fluid.
- visible streaks produced in a transparent medium as a result of variations in the medium's density leading to variations in refractive index. They can be recorded by flash photography (schlieren photography)
- streaks or platelike masses of mineral in a rock mass, that differ in texture or composition from the main mass
