Question

How can a refractometer be used to identify gemstones?

Answer 1

A refractometer measures the refractive index of a material, i.e. the amount of breaking of a ray of light. Of course the material has to be transparent.

Explanation:

All materials have a specific refractive index (`n`). For common glass this is in the neighbourhood of 1.5, special glass can have an `n` up to 1.9. Diamond is around 2.4.
By comparing the `n` of the material with the `n` of known gemstones, they can be identified or excluded.