Why are some stones referred to as precious and others as semi-precious?

Question

why is a diamond or a ruby considered precious where as an amethist is only considered semi-precious?

Answer 1

This is a totally outdated description for stones and has, in fact, been banned from use by most of the worlds gemstone traders and jewellers associations.

For example by the old method chrysoberyl is classed as semi-precious however alexandrite (the colour change variety of chrysoberyl) can sell for $25,000 per carat - which is hardly "semi" by any standard.

Answer 2

It's done through a lot of things; colour, clarity, commonality, the way the crystals are structured.  Plus there's a weight of history behind it that 'says' one is precious and the other not so we follow along like good little soldiers.

  Not to mention that they're all sparkly and pretty n stuff and people will do a lot for the promise of one.

Answer 3

It is based on their availability - the more abundant a stone (or gem) is, the less value it has.  Of course all of them must be attractive in some way.