List of refractive indices

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**Some representative refractive indices**
Material	n at f=5.09x10¹⁴ Hz
Vacuum	1 (exactly)
Helium	1.000036
Air @ STP	1.0002926
Carbon dioxide	1.00045
Water Ice	1.31
Liquid Water (20°C)	1.333
Cryolite	1.338
Acetone	1.36
Ethanol	1.36
Teflon	1.35 - 1.38
Glycerol	1.4729
Acrylic glass	1.490 - 1.492
Rock salt	1.516
Crown glass (pure)	1.50 - 1.54
Salt (NaCl)	1.544
Polycarbonate	1.584 - 1.586
Flint glass (pure)	1.60 - 1.62
Crown glass (impure)	1.485 - 1.755
Bromine	1.661
Flint glass (impure)	1.523 - 1.925
Cubic zirconia	2.15 - 2.18
Diamond	2.419
Moissanite	2.65 - 2.69
Cinnabar (Mercury sulfide)	3.02
Gallium(III) phosphide	3.5
Gallium(III) arsenide	3.927
Silicon	4.01

Many materials have a well-characterized refractive index, but these indices depend strongly upon the frequency of light. Therefore, any numeric value for the index is meaningless unless the associated frequency is specified.

There are also weaker dependencies on temperature, pressure/stress, et cetera, as well on precise material compositions (presence of dopants et cetera); for many materials and typical conditions, however, these variations are at the percent level or less. Thus, it is especially important to cite the source for an index measurement if precision is required.

In general, an index of refraction is a complex number with both a real and imaginary part, where the latter indicates the strength of absorption loss at a particular wavelength—thus, the imaginary part is sometimes called the extinction coefficient k. Such losses become particularly significant, for example, in metals at short (e.g. visible) wavelengths, and must be included in any description of the refractive index.