The term gemstone is applied to any of the one hundred or so naturally occurring minerals (diamond, ruby, sapphire, etc.) and organic materials (amber, pearls, ivory, coral, etc.) that are used for personal adornment or display. However, most of the popular gem materials encountered today are inorganic. The first use of a mineral or organic substance for personal adornment remains the subject of debate. But it is generally accepted that their use dates back at least ten thousand years.
To be classified as a gemstone, an organic or inorganic material must possess beauty, rarity, and durability. A gem’s beauty comes from its brilliance, fire, luster and color. In their rough form these attributes are often masked. Only after cutting and faceting and often other enhancements, can the true beauty be revealed. Durability refers to a combination of the material’s hardness (ability to withstand scratching), toughness (ability to resist breakage), and stability (ability to withstand chemical or physical change resulting from heat, light or chemical exposure).
There are approximately 2,700 different minerals on record. However, less than one hundred are regarded as a gemstone or ornamental variety for jewelry use and fewer than 50 are regarded as common. Gems are grouped by their composition and classed by species and variety. Minerals form at different depths within the Earth. Some form close to the surface when solutions containing minerals and water experience a change (usually the evaporation of water) triggering the crystallization process. To illustrate this process one can dissolve salt into warm water. Let the water stand for a few weeks at room temperature and as it evaporates the salt crystals will form as the amount of water diminishes to a level where the salt can no longer be held in solution. Most gem varieties formed at depth from the elements present in the Earth’s mantle. Initially these elements may be contained in molten mixtures called magma. As the molten material was forced closer to the Earth’s surface by various processes, the mixtures cooled and minerals crystallized. Because silicon, oxygen and quartz are abundant in the Earth, it is no surprise that most gems are silicates, oxides and quartzes.