admin answers:
Precious stones vs. Semi-precious stones is not a scientific categorization. Traditionally, the precious stones--which included diamond, ruby, sapphire, emerald, and amethyst--were much harder to obtain than other gemstones, like hematite, quartz, jade, carnelian, turquoise, etc.
Because of their rarity, the precious stones cost a great deal more, so they were out of reach of the common people. Their use was confined to the nobility and the clergy, which increased their mystique.
But "rarity" changes. In the 19th century, huge deposits of amythest were found in South America, and the value dropped significantly. It is no longer considered a precious stone, although some colorations, like the rare Russian Blue, are still extremely valuable. In addition, modern mining techniques make diamonds very common, however their introduction to the market is controlled so that their value and price are kept high.
