Should a top-grade tanzanite that is worth more than a diamond be considered a precious or semi-precious stone? And if a 1ct sapphire is the same price as a 5ct opal, which is a better buy? These questions and more on the preciousness or semi-preciousness of a gem have haunted many a prospective buyer, so much so that the American Gem Trade Association has banned the use of the word “semi-precious” when describing gemstones.

Most professional gemmologists no longer classify gems with this term, but it is deeply entrenched in our lingo and still used by trade organisations across the world.

In this age, only diamonds, rubies, sapphires and emeralds are acknowledged as precious stones, with the diamond chief among them and all others classified as semi-precious. The terms “precious” and “semi-precious” first came about in the mid-19th century in the West, which explains why jade, despite being enormously important and valuable in China, was never considered a precious stone. Before this distinction, practically all gems were considered precious.

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In fact, the term “semi-precious” was created mainly because of amethyst. The stone was once adored by royals until large deposits were found in South America and its commercial value drastically dropped. A new term was then required to describe its downgraded status. Other gems such as aquamarine, topaz, tiger’s eye and opal have also suffered the same fate.

Tanzanite is famously rare and supplies are expected to run out in 25 years. A good black opal can command US$8,000 per carat and the large ones fetch millions, such as the Royal One, a stunning 306ct black opal worth US$3 million. In terms of beauty, spinels were historically indistinguishable from rubies until the 19th century and equally adored. Queen Victoria’s Black Prince’s Ruby, set in the Imperial State Crown of England above the Cullinan II diamond, is in fact a giant spinel.

“Whatever category the stone is, if you want the best or the exceptional, it has a price. You have very expensive aquamarines, peridot, tourmaline, rubellite and spinel, because they are rare,” cautions Pierre Rainero, image and heritage director of Cartier.

Traditional definitions of preciousness fail to take into account the question of quality – usually based on a stone’s colour and clarity. Experts such as Melvyn Kirtley, chief gemologist at Tiffany & Co, recommend not being influenced by labels like “precious” or “semi-precious”, but instead going for stones that are the best of their kind.

I don’t like to think of a ‘hierarchy’ in gemstones, Mother Nature has given us some unique and unusual treasures in all the various species

“I don’t like to think of a ‘hierarchy’ in gemstones. Mother Nature has given us some unique and unusual treasures in all the various species. It’s finding them that is the most difficult task. I look for beauty, quality and rarity within a species. Those gemstones that exhibit the finest qualities in a species and are extraordinarily rare with an exceptional personality,” he says.

The stones that are considered precious have changed over time, so a semi-precious stone now might be considered precious in the future. When it does, the top-quality ones will be the most sought after. In fact, all top-quality stones have the potential to be recognised as precious.

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An alternative system of classification is to focus on the jewellery itself and not just the stones. Fine, semi-fine and fashion jewellery are categorisations that seem to focus on the metals in concert with the stones. Fine jewellery refers to pieces set in gold or platinum with high-grade stones and is expected to last through generations. Semi-fine indicates jewellery that is made with high quality metals like silver and might be gold-plated, and set with genuine stones. Such pieces are durable but might not be expected to last a lifetime. Fashion jewellery is made from bronze, brass or copper and is set with crystals, glass or beads.

So will the “precious” and “semi-precious” classifications ever fade away? With evermore sophisticated buyers, it seems like they already are. “We believe that these traditional hierarchies will tend to disappear where collectors and clients become more expert and appreciate many different stones for their own quality,” says Van Cleef & Arpels’ CEO, Nicholas Bos.

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Gubelin Academy’s managing director Helen Molesworth disagrees. She says that among coloured gems, “rubies, sapphires, emeralds will always be the ‘Big Three’ from gemmological but also historical perspectives. They have great physical qualities as well as being known for a very long time, which adds confidence and emotional value.”

Stocks of the Big Three are depleting, causing prices to rise. However, as other gems like tanzanite, mandarin garnet and Paraiba tourmaline increase in price, stature and popularity to fill the resulting gap, it seems unsuitable to continue to label them as merely semi-precious. Perhaps what is needed is a greater vocabulary for the preciousness of stones.