Gem Mines

Gems or gemstones are minerals, which are used for jewelry. Because of their transparency and colour they are used for aesthetic artworks. There are also some that produce extraordinary light effects, such as opal. Because of their rareness they are of some value and sometimes used as a sort of alternative currency.

Gems were divided into two groups, precious or semiprecious gems. Semiprecious minerals have a lower hardness and resistance against acids and other substances, also they are generally more common, and thus their value is lower. Many variations of quartz in particular were regarded as semiprecious stones. However, the term is outdated and is hardly used any more, mainly because the two groups cannot be reasonably defined. There were semiprecious stones that were rarer and harder than some precious stones.

Because of their hardness and resistance to acids, gemstones remain intact when the surrounding rock is dissolved by weathering. They remain almost unchanged in the loose, weathered remains of the rock, typically soft sands or clays. They are called placer deposits or alluvial deposits, and are mined in open casts and by washing the sediments. But there are also some underground gemstone mines that are of some interest. Diamonds in particular are often mined underground.