Precious vs Semi-Precious Gemstones: What the Labels Really Mean

Jewelers still sort gemstones into two groups. Diamond, ruby, sapphire and emerald are called precious, and everything else is called semi-precious. The split is old, and it does not grade quality on its own, but it still points to something real: the best natural precious stones are far rarer, harder-wearing and more valuable than almost any other gem. This guide explains where the labels came from, what the price and auction data show, and how to judge any stone, using gems from our own Toronto studio.

Where the labels came from

For centuries, gem dealers spoke of the "cardinal gems": diamond, ruby, sapphire, emerald and amethyst. Amethyst lost its place in the 1800s, when huge deposits in Brazil made fine purple quartz plentiful and its price fell. The remaining four became the precious stones, and in the 19th century the trade began calling everything else "semi-precious."

The four precious stones come from just three minerals:

• Diamond is pure carbon, the hardest natural material (10 on the Mohs scale).
• Ruby and sapphire are both corundum, aluminium oxide, hardness 9. Traces of chromium make ruby red. Iron and titanium make sapphire blue, and other trace elements give pink, yellow, orange and purple sapphires.
• Emerald is beryl coloured green by chromium or vanadium, hardness 7.5 to 8. Its cousins aquamarine and morganite are beryl too, but neither is counted as precious.

Why natural precious stones hold more value

The research is consistent: at comparable quality, natural precious stones sell for many times more than semi-precious stones and hold that value better. Four reasons stand out.

1. Rarity

Gem-quality ruby, sapphire and emerald need unusual geology to form. Ruby, for example, needs chromium in a rock that is low in silica, a combination that is uncommon in the earth's crust. Clean, richly coloured crystals large enough to cut are a tiny share of what is mined. Quartz (amethyst and citrine) and common garnet, by contrast, are found on every continent in large volumes.

2. Price per carat

Typical market prices show the gap clearly:

Price grows faster than size for precious stones, because large clean crystals are so scarce. A 5 ct fine ruby costs far more than five 1 ct rubies.

3. Auction records

At the very top of the market, only precious stones command these prices:

• The Sunrise Ruby, a 25.59 ct Burmese ruby, sold at Sotheby's Geneva in May 2015 for about US$30.3 million, roughly US$1.18 million per carat, a world record for a ruby.
• The Blue Belle of Asia, a 392.52 ct untreated Ceylon sapphire, sold at Christie's Geneva in November 2014 for about US$17.6 million.
• The Aga Khan Emerald, about 37 ct, sold at Christie's Geneva in November 2024 for about US$8.8 million, the highest price ever paid for an emerald at auction.

No amethyst, garnet or citrine has come anywhere near these figures.

4. Durability and documentation

Ruby and sapphire, at hardness 9, resist scratches from everyday dust and grit (which is mostly quartz, hardness 7), so they keep their polish for generations. Precious stones are also the stones that major laboratories such as GIA, AGL, SSEF and Gübelin report on in detail, with origin and treatment findings. A lab report makes a stone easier to insure, resell or pass down, which supports its long-term value.

One honest caveat: quality still matters most. A cloudy, poorly cut ruby is worth less than a top garnet, and a few rare "semi-precious" gems, such as red spinel, copper-bearing Paraíba tourmaline and green demantoid or tsavorite garnet, can reach the prices of fine sapphire. But compare like with like, and natural precious stones lead.

The wider world of gemstones

Semi-precious does not mean second-rate. These gems offer colour and character at a lower price, and some are genuinely scarce.

• Garnet is a family of related minerals, hardness 6.5 to 7.5. Red almandine, pyrope and rhodolite are affordable and almost never treated, which makes garnet a very honest gem. Green demantoid has more fire (dispersion) than diamond.
• Opal is a non-crystalline form of silica that holds water, hardness 5.5 to 6.5. Its play-of-colour comes from tiny silica spheres that split light into flashes of colour. Many Ethiopian opals are hydrophane, meaning they absorb water and can look different until they dry out, so keep them away from soaking, oils and sudden heat.
• Tanzanite is the gem variety of the mineral zoisite, found commercially in only one place on earth: the Merelani Hills of northern Tanzania, discovered in 1967. Most blue-violet tanzanite has been heated. Unheated or naturally coloured material shows soft yellows, peaches, greens and lavenders, often sold as multicolour tanzanite. It is trichroic, showing different colours from different angles, and at hardness 6 to 7 it suits earrings and pendants best.

Treatments: the question that changes the price

Most coloured stones are treated in some way, and the type of treatment matters as much as the species.

• Heat only is the most common treatment for ruby and sapphire. It is permanent and widely accepted, and it should always be disclosed. The rubies pictured above are heated.
• Unheated rubies and sapphires are rarer and sell at a clear premium, usually backed by a lab report.
• Oil or resin is routine for emerald. The amount matters: "minor" oil is accepted, while heavy filling lowers value.
• Glass filling in ruby and sapphire hides large fractures with lead glass. These stones cost a small fraction of untreated or heated ones and need gentle care.

Our guide to gemstone treatments explains each term in more detail.

How experts judge any gemstone

1. Colour matters most. Look for strong, even colour that is neither too dark nor washed out.
2. Clarity is judged by gem type. GIA groups coloured stones into three clarity types: Type I stones such as aquamarine and tanzanite are usually eye-clean, Type II stones such as ruby and sapphire usually show some inclusions, and Type III stones such as emerald almost always do. An emerald with visible garden-like inclusions (the trade calls it "jardin") can still be very fine.
3. Cut should bring the colour to life with no dull window in the centre.
4. Carat weight: price per carat rises with size, steeply so for precious stones.
5. Origin can add a premium, for example Burmese ruby, Ceylon sapphire and Colombian emerald, but only when a lab report supports it.
6. Treatment: always ask, and get it in writing.

Hardness, toughness and care

Hardness is resistance to scratching. Toughness is resistance to chipping and breaking, and the two are not the same. Emerald is fairly hard but brittle because of its inclusions, and diamond can chip along its cleavage planes despite being the hardest gem.

• Everyday rings and bracelets: diamond, sapphire and ruby.
• Earrings and pendants: emerald, tanzanite, garnet, amethyst and aquamarine.
• Special-occasion pieces: opal and pearl.
• Cleaning: warm water, mild soap and a soft brush are safe for every stone. Avoid ultrasonic and steam cleaners for emerald, opal and tanzanite.

Our approach at Roho Jewels

We hand-select natural, earth-mined gemstones in Toronto. Every treatment is disclosed on the listing, and every stone carries our lifetime guarantee that it is natural and genuine. Browse our rubies, sapphires, emeralds and loose gemstones, or contact us for help finding a centre stone.

Sources

• Guinness World Records: most expensive ruby per carat (Sunrise Ruby)
• Guinness World Records: most expensive sapphire (Blue Belle of Asia)
• Guinness World Records: most expensive emerald sold at auction (Aga Khan Emerald)
• Ceylons: how much do different gemstones cost?
• FossilEra: what is amethyst worth?
• RubyGlint: garnet price per carat

Prices are typical market ranges for loose stones and vary with quality, size and origin. They are a guide, not an appraisal.