Glorious Collection of Emerald Jewelary

The traditional classification in the West, which goes back to the Ancient Greeks, begins with a distinction between precious and semi-precious stones; similar distinctions are made in other cultures. The precious stones are diamond, ruby, emerald and sapphire, with all other gemstones being semi-precious. This distinction is unscientific and reflects the rarity of the respective stones in ancient times, as well as their quality - all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8-10 on the Mohs scale. Other stones are classified by their color, translucency and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called Tsavorite, can be far more valuable than a mid-quality emerald.Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone.

Aside from the diamond, the ruby, sapphire, emerald, pearl (strictly speaking not a gemstone) and opal  have also been considered to be precious. Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a precious stone as well, going back to ancient Greece. Even in the last century certain stones such as aquamarine, peridot and cat's eye have been popular and hence been regarded as precious.