- A rock sample cut from a borehole or retrieved from the sea floor. See core analysis.
- The Earth's core is the central portion bounded by the Gutenberg discontinuity (≈2900 km deep) that separates it from the mantle. The core’s radius is ≈3500 km; it is presumed to be composed predominantly of iron and silicates. See Figure E-1. Divided into outer core (which will not transmit S-waves) and inner core, the radius of the inner core being about 1220 km. The inner core was discovered by Inge Lehmann in 1936.
- A material of high magnetic permeability placed in the center of a coil of wire. Used in the flux-gate magnetometer for measuring magnetic fields.
- A magnetic core (q.v.) is a device that used to be used in rapid-access memories.