What causes the lustre of a metal?

The lustre of a metal is due to the presence of mobile (free) electrons in it.


The free electrons can move freely in the metal, causing any light incident to reflect. This reflection is a specular reflection rather than diffused, and thus the metal surface appears shiny or lustrous.

  • Minerals produce metallic lustre with a refractive index of greater than 3. The minerals are opaque and usually are from the native element and sulphide groups.
  • Adamantine lustre is the brilliant lustre produced by minerals such as diamond—the refractive indexes for this lustre range from 1.9 to 2.6.
  • Vitreous lustre is the lustre of glass. The refractive indexes range from 1.3 to 1.9.
  • Diamonds have a greasy lustre which is caused by the slight roughness of the surface.

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