Most American and European gold jewellery is made of an alloy of gold, the purity of which is stated in karats, indicated by a number followed by the letter K. American gold jewellery must be of at least 10K purity (41.7% pure gold), (though in England the number is 9K (37.5% pure gold) and is typically found up to 18K (75% pure gold). Higher purity levels are less common with alloys at 22 K (91.6% pure gold), and 24 K (99.9% pure gold) being considered too soft for jewellery use in America and Europe.

The British crown jewels contain the Cullinan Diamond, part of the largest gem-quality rough diamond ever found (1905), at 3,106.75 carats (621.35 g). Now popular in engagement rings, this usage dates back to the marriage of Maximilian I to Mary of Burgundy in 1477. Other gemstones:Many precious and semiprecious stones are used for jewellery. Among them are:

Ruby: Rubies are known for their intense red colour, and are among the most highly valued precious gemstones. Rubies have been treasured for millennia. In Sanskrit, the word for ruby is “ratnaraj”, meaning “king of precious stones.”

Amethyst: Amethyst has historically been the most prized gemstone in the quartz family. It is treasured for its purple hue, which can range in tone from light to dark. Emerald: Emeralds are one of the three main precious gemstones (along with rubies and sapphires) and are known for their fine green to bluish green colour. They have been treasured throughout history, and some historians report that the Egyptians mined emerald as early as 3500 BC.

Many items of jewellery, such as brooches and buckles originated as purely functional items, but evolved into decorative items as their functional requirement diminished. Jewellery can also be symbolic of group membership, as in the case of the Christian crucifix or Jewish Star of David, or of status, as in the case of chains of office, or the Western practice of married people wearing a wedding ring.

Although artistic display has clearly been a function of jewellery from the very beginning, the other roles described above tended to take primacy. It was only in the late 19th century, with the work of such masters as Peter Carl Faberge and Rene Lalique, that art began to take primacy over function and wealth. This trend has continued into modern times, expanded upon by artists such as Robert Lee Morris and Ed Levin.

These high purity alloys, however, are widely used across Asia, the Middle East, and Africa. Platinum alloys range from 900 (90% pure) to 950 (95.0% pure). The silver used in jewellery is usually sterling silver, or 92.5% fine silver. In costume jewellery, stainless steel findings are sometimes used.

Wearing of amulets and devotional medals to provide protection or ward off evil is common in some cultures; these may take the form of symbols (such as the ankh), stones, plants, animals, body parts (such as the Khamsa), or glyphs (such as stylized versions of the Throne Verse in Islamic art).