opal

Several species of marine mollusks produce stony growths called calcareous concretions or non-nacreous pearls. Varieties such as conch pearls,…

Like their marine cousins, many freshwater mollusks can produce pearls. However, this rarely occurs in nature. Today, the majority of pearls…

Ammolite is a rare, iridescent, gem-quality material cut from the fossilized shells of extinct sea creatures. Found only in the Bearpaw Formation…

Although pearls are one of humanity’s most ancient gems, natural undersea beds of pearl-producing oysters now occur very rarely. Cultured…

Made from two or more materials, assembled gems can make durable and affordable jewelry. Learn more about gemstone doublets, triplets, and other…

An assembled gemstone is constructed from two or more combined materials. Gemstone doublets and triplets, intarsias, and rhinestones are all…

Some beautiful gems, like pearls, opals, and tanzanites, are very vulnerable to impacts and scratches, especially when worn on rings. Even more…

This table contains a selection of minerals gemologists may encounter as jewelry stones or gem specimens. The gems are sorted by their crystal…

Measuring specific gravity helps gemologists identify gemstones. The following table lists the specific gravity values for a variety of gem…