What causes the lustre of a metal?

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

Explanation

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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