The Difference Between Precious & Semi-Precious Stones

History of Classification

• Historically, gemstones were considered semi-precious when they could be found in abundance. Precious gemstones were those stones that were not found as easily and were thus considered rare. Professional gemology today does not use the terms "precious" and "semi-precious." Gemologists have shown that a stone that was once classified as precious is not necessarily more valuable than a semi-precious stone. For example, a small and flawed diamond may be worth far less than a large and clear opal.

Classification's Use

• While the difference between precious and semi-precious gemstones has not always been a clear line, generally, the harder to find the stone, the more precious and valuable it is. Collectors and merchants used the classification to determine worth and invested value, and vice versa. For example, amethyst was once considered a precious stone, but when a large quantity of the stone was found in Brazil and Uruguay, it was relabeled as a semi-precious stone, and its value dropped.

Composition

• Precious and semi-precious gemstones are composed of minerals with a unique molecular structure. The difference among all gemstones, precious and semi-precious, is the chemistry within the stones. For example, diamonds and graphite are both completely made of carbon atoms, but their individual molecular structures are so different that one is destined for an engagement ring while the other is used as pencil lead. The actual composition of a stone does not determine its classification as precious or semi-precious, but rather its classification as an individual gem.

Precious vs. Semi-Precious Stones

• The gemstones considered precious are diamonds, rubies, sapphires and emeralds. All other gemstones are classified as semi-precious. Organic materials that are not naturally occurring in rock, such as pearls and amber, are also sometimes referred to as semi-precious stones. Some gemologists classify gemstones as either diamonds (including colored diamonds) or colored stones. This is because diamonds require special tools for mining and cutting. Colored stones are all the gemstones that are not diamonds.