Jet is a geological material that is not considered a mineral in the true sense of the word. It is a hard, compact variety of lignite, coal-black in color. It is easily polished and has been used in the manufacture of cheap ornaments.
A jet is a stream of fluid produced by discharge through an orifice into free space.
Since gas is a compressible fluid, the velocity attained by a jet of gas cannot be determined by Bernoulli's principle. Instead, if one uses adiabatic expansion from P1 to P2 in a properly shaped nozzle, the ideal velocity of a gas jet is:
- v = 8×√((RT1/z)×(1-(P2/P1)z))
Jet is commonly used as a description, usually referring to the soot that accumulates at the back of a jet engine. EG: "Jet Black".